Uh oh!
So, you just bought your new fish and are only just now learning about this cycling thing…
Or, maybe you are following the terrible advice of the pet store employee who said you only need to run your filter for 24 hours before adding your fish.
Maybe it’s even worse. You killed all the good bacteria in your tank and have to cycle your aquarium all over again.
Don’t worry! These scenarios are much more common than you think.
If you can’t return your fish, then you have only one option:
You have to cycle your aquarium the old-fashioned way – with fish in the tank.
Today, I am going to show you how to successfully cycle your aquarium with fish inside.
If you haven’t bought your fish just yet, I recommend using the fishless cycle, which is an easier, faster and safer way to cycle your aquarium. Interested? FishLab’s fishless cycling guide will walk you through the process.
Contents
- What is fish-in cycling?
- Why shouldn’t you use a fish-in cycle?
- The secret to successfully cycling with fish in your tank
- Essential products to perform a fish-in cycle
- How do you perform a successful fish-in cycle?
- What’s next? Life after cycling
What is fish-in cycling?
The purpose of a fish-in cycle is to kick-start the nitrogen cycle, an invisible three-stage process where beneficial (good) bacteria establish themselves in your filter, keeping your fish safe from ammonia.
I cover the nitrogen cycle in much greater detail here. If you are new to the hobby, it’s worth reading because an effective nitrogen cycle is perhaps one of the most important parts of a healthy tank.
For the rest of you, here’s a quick recap of the nitrogen cycle in action…
Stage 1 Waste such as pee, poop and uneaten fish food break down, releasing ammonia, a toxic chemical, into the water.
Stage 2 Beneficial bacteria eat the ammonia and release nitrites, yet another toxic chemical.
Stage 3 A second type of beneficial bacteria eat the nitrites and convert them to nitrates, which are harmless in small amounts and are removed from your aquarium each time you perform a water change.
Just one problem…
There aren’t any beneficial bacteria in a brand new aquarium. And without it, toxic ammonia and nitrites build up, causing serious harm to your fish…
So, it’s up to you to kick-start the nitrogen cycle. And to do that, you need some help from your fish, well from their pee and poop.
As the poop breaks down, it releases ammonia and encourages the beneficial bacteria to appear.
You might have noticed a flaw in this…
If ammonia is harmful to fish, and you are using your fish as a source of ammonia, doesn’t this harm them?
Well, that’s exactly what brings me to my next point…
Why shouldn’t you use a fish-in cycle?
In an emergency, a fish-in cycle might be your only option. If that’s the case, cycling with fish is perfectly acceptable because your fish might die if you don’t.
But if you have a choice, then you shouldn’t be cycling your aquarium with fish inside.
Why?
Well, a picture says it best…
Yep, fish-in cycling is very stressful for your fish. And, many fish won’t survive the process. Those that do are often more susceptible to disease and live shorter lives.
I assume you want to keep your pet fish alive as long as possible, right? Well, a fish-in cycle is a terrible way to start.
So, why is a fish-in cycle so harmful to fish?
Well, during the cycling process you are waiting for beneficial bacteria to establish a colony in your aquarium. And once they do, they will be able to eat ammonia and nitrites as quickly as they are produced.
Just one problem…
While you are waiting for the bacteria to grow in numbers, your fish are going to be exposed to elevated levels of ammonia and nitrites. Even at low levels, these toxic substances can stress and severely irritate your fish.
Not only that, but a fish-in cycle requires delicate planning and leaves little room for error. It’s not exactly beginner-friendly.
Now… I’m not trying to say that fish-in cycling doesn’t work. It certainly can. But considering the obvious harm that it can cause your fish, it should only be done in an emergency.
To be honest, given that you can now cycle your aquarium without fish, it’s puzzling to see the dated fish-in cycle still being recommended.
So, why do people continue to give the advice that it’s okay to cycle your aquarium with fish in it?
I was chatting with my local, big-box pet store the other day, and the employee was preaching the wonders of fish-in cycling. I would also like to point out that he was trying to convince me to buy fish to go with my new aquarium.
The reason was pretty clear… An extra sale. A pretty scummy move, right?
But in other cases, the advice to cycle with fish is much less sinister.
You see, fish-in cycling is how your grandparents would have cycled their tank. Yep, this method has been in use for that long. In fact, this was the only way to cycle a tank back then.
In these instances, the advice to go with a fish-in cycle came from the best of intentions, people passed on what they learned years ago. You can’t fault them for that. But you can fault them for not keeping up with the times! Fortunately, you now know better!
Look, I’m sure some of you are going to disagree with me on this. Maybe you have successfully used a fish-in cycle hundreds of times without harm. That’s cool too…
But for a beginner, a fishless cycle is by far the best way to go. And in this case, a fish-in cycle should only be used when absolutely necessary.
The secret to successfully cycling with fish in your tank
I’m going to let you in on a little secret…
You can tell whether your fish-in cycle is going to be a success or failure before you even begin.
Seriously.
And, it all comes down to the number of fish you have in your aquarium.
More fish = more poop and pee
Since this waste breaks down into ammonia, your ammonia levels are going to rise rapidly.
And the faster your ammonia levels rise, the more harm done to your fish.
So, what is the correct number of fish to use in a fish-in cycle?
Obviously, this aquarium is too small for the number of fish…
The larger your aquarium, the more fish you can include in a fish-in cycle.
Rule of thumb: One fish for every 10 gallons of water.
So, if your tank is 1 gallon, only 1 fish. If your tank is 58 gallons, 5 fish.
Don’t know your tank size? Use FishLab’s gallon calculator.
But what if you have more fish than should be in your tank?
Ideally, you want to do one of the following:
1. Give your fish away – Either return your fish, give them to a friend or contact your local fish club to see if anyone will take them.
2. Buy a larger tank – Buying a larger tank will increase the amount of fish you can cycle with.
But what if neither of these is an option?
Well, unfortunately it’s time for you to make a judgment call.
Do you try and cycle your aquarium with all your fish inside and risk killing them all?
Or, do you euthanize some, giving the rest a much greater chance of survival?
It’s a tough decision that only you can make.
Decided to euthanize? Please read FishLab’s guide to humanely killing fish. If you have to do it, please do it correctly.
Essential products to perform a fish-in cycle
In addition to your fish, tank and equipment like filters and heaters, you need two very important products to ensure that your tank is cycled correctly…
1. An aquarium test kit
The problem with the nitrogen cycle is that you can’t see it. The only way to monitor the cycling process is to test for it. And to do that, you need a good aquarium test kit.
I recommend buying a master test kit like the one pictured above because it includes all the test kits you need to cycle your aquarium at one low price.
To learn how a test kit works, check out FishLab’s aquarium test kit guide.
2. Water conditioner
Or more specifically, Seachem Prime. I consider it to be the best aquarium water conditioner available.
Get to know this product. During a fish-in cycle, it’s going to be your best friend.
Seachem Prime serves two purposes. The first is making your tap water safe…
You see, tap water contains chloramine and chlorine, two chemicals. Not only are these chemicals toxic to fish, but they also kill that beneficial bacteria. And without that, your tank won’t cycle.
Fear not! A dose of Seachem Prime to your tap water before adding it to your aquarium will dechlorinate your water, making it safe for the beneficial bacteria and the fish when you finally add them.
Seachem Prime also has the added benefit of neutralizing ammonia, nitrites and nitrates in your aquarium for 24 to 48 hours, making them harmless to your fish.
With these two products on hand, you are now ready to begin.
How do you perform a successful fish-in cycle?
Before I continue, I want to make one thing clear:
The lives of your fish are at stake!
It’s important that you carefully follow this guide. Read each step twice if you have to. Make sure you completely understand what you are doing before proceeding.
I cannot guarantee that your fish will survive the cycling process – some are more sensitive than others. But by following this guide, you give them the best possible chance.
When it comes to fish-in cycling, you have two choices – cycling with Seachem Prime or with water changes.
A) Fish-in cycling with Seachem Prime
If you are a beginner or are just looking for the easiest way to perform a fish-in cycle, then choose this option. This method uses daily dosing with Seachem Prime to render ammonia, nitrites and nitrates harmless to your fish.
The advantage is that you will perform fewer water changes.
Jump to these instructions for a Seachem Prime fish-in cycle.
B) Fish-in cycling with water changes
If you want to use fewer chemicals, you can perform a fish-in cycle just with water changes. This method uses the diluting effects of fresh water to keep ammonia, nitrites and nitrates at a low level.
Note: This method of fish-in cycling still requires a bottle of Seachem Prime or other water conditioner to dechlorinate your tap water. It’s also nice to have on hand in an emergency – in case something goes wrong.
Jump to these instructions for a water-change focused fish-in cycle.
Performing a fish-in cycle with Seachem Prime
Step 1: Set up your aquarium
It’s time to set up your aquarium. And, that includes all the equipment – heaters, filters, air pumps… Get it in there! Don’t forget to rinse it with fresh water first!
The beneficial bacteria need a surface to cling to, namely your substrate and filter media. So by setting everything up, you give your bacteria as many surfaces as possible to cling to.
Add water to the tank, and don’t forget to dechlorinate it with your water conditioner first.
Finally, you want to keep all electrical equipment, such as heaters, filters and bubblers, switched on throughout the entire cycling process. Not only will this keep your fish as comfortable as possible, but it will also make your tank cycle faster.
Want to cycle your tank as quickly as possible? Check out FishLab’s tips for speeding up the cycling process.
Step 2: Adding your fish
Before you add your fish, you want to acclimate them first. This will give them the best chance of survival.
You want to feed your fish throughout the cycling process… You don’t want them to starve!
When feeding your fish, however, it’s important that you don’t feed them too much. The more you feed them, the more they are going to poop. And the more they poop, the faster your ammonia levels are going to rise.
Also, remove any uneaten food from the tank, a good aquarium net will make this easy. Any uneaten food left behind will break down into ammonia, causing the levels to rise.
If a fish dies during the cycle, remove it from the aquarium ASAP. Its decaying body will also give off ammonia. Don’t panic if one of your fish dies. It doesn’t necessarily mean that all your fish will – this one might have been extra sensitive.
Step 3: Test, test, test, and test again
Now, use your ammonia test kit every 24 hours.
What you are looking for is any sign of ammonia. Trust me. It won’t be long before it appears.
Once your test kit returns positive for ammonia, it’s time to move to the next step.
Step 4: Dealing with ammonia
Once you detect ammonia, it’s time to start dosing with Seachem Prime. Follow the instructions on the bottle to determine what a single dose would be for your tank – the larger the aquarium, the more Prime you will need.
Fortunately, a little goes a long way, and many of you will find that a single bottle of Prime will get you through an entire cycle.
For this method, Seachem Prime is the most important ingredient. You see, a dose of Prime will bind ammonia, nitrite and nitrate for 24 to 48 hours, making them harmless to your fish.
Picture Seachem Prime locking up ammonia, nitrite and nitrate in a jail cell for up to 48 hours. While in the cell, these nasties cannot harm your fish. However, once their time is up, and they are released, they will once again attack your fish.
It is for this reason that you need to dose regularly with Seachem Prime, to keep these nasties locked up.
A single dose of Prime will treat up to 1 part per million (ppm) of ammonia. Prime can be dosed up to 5 times safely. So, 2 ppm of ammonia can be treated with two doses of Prime, 3 ppm can be treated with three doses, and so on.
Anything less than 1 ppm should be treated with a single dose. Between 1 ppm and 2 ppm, two doses. You get the idea. Oh, and it goes without saying that it’s better to overdose than underdose.
Keep dosing and using your aquarium test kit daily. At this stage, you need to perform a 50% water change.
Once your test kit reads 2 ppm of ammonia, you should perform a 50% water change. This should cut your ammonia levels roughly in half.
Repeat this process until you notice that your ammonia levels are not rising as quickly as before. Typically, this will take a week or two. When this happens, you are ready to move to the next step.
Step 5: Nitrites start to appear
Next, you need to test for nitrites. If none are present, keep repeating the previous step and testing for nitrites daily until you get a positive result.
Now that nitrite has entered the equation, you need to make sure you are dosing with enough Prime to protect your fish from both ammonia and nitrites.
Fortunately, working out your new dosage is pretty simple – just add your nitrite and ammonia readings together.
Let’s say your test returns the following…
| Ammonia | 0.25 ppm |
| Nitrite | 1.5 ppm |
Adding the two together will give you a total of 1.75 ppm. A double dose of Prime will take care of it.
This time, if your combined ppm of ammonia and nitrite reaches 4, perform a 50% water change.
Keep repeating this. You will eventually notice that your ammonia drops to zero. This is a good thing – bacteria are eating the ammonia as quickly as it is being produced, resulting in a zero reading.
Continue daily dosing and testing for ammonia and nitrites. Once your nitrite levels stop rising as quickly, you are ready for the next step.
Step 6: Nitrates appear
Now, you want to test for nitrates. If none are present, keep repeating the previous step and testing for nitrates daily until you get a positive result.
Once nitrates are present, you are nearing the end (woohoo!). Continue testing for ammonia, nitrites and nitrates. Your ammonia levels should still be zero, and your nitrite levels should be declining.
Keep dosing with Prime until both your nitrite and ammonia levels are zero. At this stage, the beneficial bacteria are eating them as quickly as they are being produced.
Congratulations! You have successfully completed a fish-in cycle.
Performing fish-in cycling with water changes
Step 1: Set up your aquarium
It’s time to set up your aquarium. And, that includes all the equipment – heaters, filters, air pumps… Get it in there! Don’t forget to rinse it with fresh water first!
The beneficial bacteria need a surface to cling to, namely your substrate and filter media. So by setting everything up, you give your bacteria as many surfaces as possible to cling to.
Add water to the tank, and don’t forget to dechlorinate it with your water conditioner first.
Finally, you want to keep all electrical equipment, such as heaters, filters and bubblers, switched on throughout the entire cycling process. Not only will this keep your fish as comfortable as possible, but it will also make your tank cycle faster.
Want to cycle your tank as quickly as possible? Check out FishLab’s tips for speeding up the cycling process.
Step 2: Add your fish
Before you add your fish, you want to acclimate them first. This will give them the best chance of survival.
You want to feed your fish throughout the cycling process… You don’t want them to starve!
When feeding your fish, however, it’s important that you don’t feed them too much. The more you feed them, the more they are going to poop. And the more they poop, the faster your ammonia levels are going to rise.
Also, remove any uneaten food from the tank. This, too, will break down into ammonia if left behind.
If a fish dies during the cycle, remove it from the aquarium ASAP. Its decaying body will also give off ammonia. Don’t panic if one of your fish dies. It doesn’t necessarily mean that all your fish will – this one might have just been extra sensitive.
Step 3: Test, test, test, and test again
Now, use your ammonia test kit every 24 hours.
What you are looking for is any sign of ammonia. Trust me. It won’t be long before it appears.
Once you notice ammonia building up, it’s time to test your aquarium twice a day. And, you need to make it a routine. If you leave the house during the day, morning and night are fine.
Step 4: Water change after water change
You want to keep the ammonia levels low, at a tolerable level for your fish. So, 0.25 parts per million (ppm) or less is your goal.
The moment you notice the ammonia levels reach 0.5 ppm, you want to perform a 50% water change. That is, remove 50% of the water from your aquarium and replace it with fresh water. Don’t forget to add the dechlorinator!
What this does is remove some of the ammonia from your aquarium, diluting it and lowering the levels.
Now, just how often you need to do this entirely depends on the size of your tank and how many fish you are cycling with.
Some of you might only need to do a water change twice a week, but others might need to do it twice a day. That’s fine. Let the test kit determine how often to do a water change.
Keep this up for at least a week before moving to the next step.
Step 5: The first beneficial bacteria appears
After a week, you will notice that your ammonia levels are not rising as quickly as they were before. This is a good sign that the first beneficial bacteria has entered your tank and is eating the ammonia, helping to keep the levels down.
To make sure that this is the case, you now want to test for nitrites. So, use your nitrite test kit. If it comes back positive for nitrites, congratulations!. You are in the first stage of the nitrogen cycle, but your work is far from finished…
Don’t worry if you don’t see nitrites yet. Simply repeat Step 4 and continue testing for nitrites until you do. Be patient. Remember… Fish-in cycling takes a lot longer than fishless cycling.
Step 6: More water changes
If anything, nitrites are more toxic than ammonia. You want to keep nitrites as close to zero as possible. And to do that, you must continue performing water changes.
Continue monitoring your ammonia and nitrites on a daily basis, and perform water changes when your nitrite levels rise.
Keep doing this for at least another week before moving to the next step.
Step 7: The second beneficial bacteria appear
After another week, the nitrite levels should not be rising as quickly as they were before. This is a good sign that the second beneficial bacteria is beginning to grow in your aquarium.
To make sure, grab your nitrate test kit. If it returns positive for nitrates, celebrate! You are on the home stretch.
Again, it can take longer than a week for nitrates to appear. Just keep repeating Step 5 until your nitrate test indicates that they are present in your tank. Patience, patience, patience. Did I mention patience?
Step 8: Continue testing and performing water changes
All that’s left to do is to keep testing, monitoring your ammonia, nitrite and nitrate levels.
If your nitrate levels creep over 40 ppm, it’s time for a water change. Although if you are performing water changes to keep your nitrites low, I’d be surprised if your nitrate levels ever reach this.
Continue this process until both the ammonia and nitrite levels read zero on the same day. Remember, the entire cycling process can take months. So again, be patient.
What’s next? Life after cycling
Woohoo!
You did it!
The beneficial bacteria in your tank are in high enough numbers that they can eat ammonia and nitrites as quickly as they are produced.
It might have taken a long time, but trust me, it was worth it!
Your tank is now safe for your fish. Any fish that survived deserve a medal of honor because they made the tank safe for any new fish you want to add.
On that note…
If you want to add more fish to your tank (assuming your tank is large enough), wait a week before adding a maximum of three. This gives the bacteria a chance to adapt to the increase in waste and grow in numbers to deal with it.
Still want to add more fish? Wait another week and repeat.
And remember, from this point on, nitrates will consistently build up in your aquarium. This is a major reason why we perform regular water changes – to keep the nitrate levels low.
Conclusion
Phew, you did it. I knew you could!
By cycling your aquarium, you give your fish the best possible chance to live a happy and healthy life.
Once the nitrogen cycle has started, it consistently runs in the background.
But you are not home free just yet…
You still need to regularly monitor your ammonia and nitrite levels to ensure that nothing goes wrong. I recommend that you include testing your tank as part of your regular water change routine.
Do you cycle your aquarium with fish inside? Let me know in the comments below!
I also use this site as an excuse to spend lots of money on testing and reviewing different aquarium products! You can find my reviews here.
Hi, it’s Taylor. I just commented about my 5 Giant Danios but I read the levels wrong.
Ammonia: 0.25 ppm
Ph: still same problem as last time
Nitrite: between 0.25-0.50 ppm, but on the lower side of that.
Nitrate: 5-10 ppm, but on the higher side of that.
Still wondering why they seem so high after I just did a water change, and not sure what to do next. Sorry for two different comments, my eyes are getting worse and worse!
Hi Taylor, it’s possible your tap water already has ammonia or nitrites in it. Have you tested your tap water to confirm?
On the ammonia front, seachem prime can cause a false positive for ammonia since the API tests measure both ammonia (dangerous) and ammonium (harmless) – when seachem prime binds ammonia, it is temporarily converted to ammonium. So while you may have a reading for it, it may not be as dangerous as you think. The only way to tell for sure is to purchase a seachem ammonia kit. Off the top of my head, this is the only aquarium test kit to test for ammonia and ammonium individually.
The nitrites are the case for concern and it’s not unusual for your nitrite levels to reach this high in a day if there is no beneficial bacteria there to “eat” them. You can either use prime or water changes to get it down.
Once those are under control, it’s a waiting game. Slowly you should see your nitrates increase as the nitrites get consumed.
Hi, I am doing a fish-in cycle right now with 5 Giant Danios and a 20 gallon tank. I tested positive for nitrites on Wednesday. I waited until Friday to do a water change because I did not have time to do it sooner, but I used Seachem Prime every day just to be safe. On Friday, I did a 40% water change using Seachem Prime again. Today, Saturday, I used the API Freshwater Master Kit to test my water levels. I came back with: (my temperature is at 75 degrees, by the way)
Ph: I’m not sure how to tell this one: I use the regular ph reagent and always come back with 7.6, the highest possible number. The kit said that if you get 7.6, to always try the high range reagent too to know the exact number, but when I use high range, I get 7.4, the lowest number. How do I know what my ph really is?
Ammonia: 0.25 ppm
Nitrite: 0.50 ppm
Nitrate: somewhere between 10-20 ppm
I didn’t think that my Ammonia, Nitrite, and Nitrate could possibly be that high since I had just done a water change the day before, so I’m not sure what’s wrong. What should I be doing at this stage?
Hi Ian, I just wanted to say hello and wish you a Merry Christmas and Happy New Year. You have been a big help and I feel as if I’ve known you for a long time. The aquarium and fish are doing well, as always thanks for everything.
Best Wishes
Steve
Haha, Hi Steve,
I’d say it’s still a little early for the seasons greetings – I still have not even gotten around to buying christmas presents or setting up a tree. But I appreciate it.
I’m super happy to hear that your fish are doing well. No need to thank me, I love to help others. Besides, you did all the hard work in figuring it out!
Wishing you all the best for the future!
The article is really useful to explain the cycle, but seems an bit too much an ad for Seachem Prime to me… because dechlorinating the tank could be done for free! Just let the water 1 day or 2, that’s all! Boiling it or adding Oxygen could make the waiting time shorter. It’s ALWAYS better to do without shop chemicals if you can avoid them.
A good advice would be to test the tap water. Some people have no heavy metals and crap in their water, so the need of a water conditioner is…zero. While some people have toxic tap water, and they have to add a water conditioner.
Another advice: never trust the petshop sellers. If they are good sellers… they lie.
Hi Li,
Some interesting advice here, but I would suggest it’s aimed at people with experience in fishkeeping rather than beginners, who are the target audience of this cycling guide.
I don’t know about you, but I don’t think it’s particularly feasible. Boiling or storing 50+ gallons of water at a time and carrying it to your tank? It’s unrealistic. For beginners, using a dechlorinator is the easiest and most recommended option.
Same goes for your advice on testing tap water for heavy metals, most aquarium master test kits do not have the ability to test for these.
Finally, I agree that big box chains like petsmart and petco are hit and miss in terms of advice, generally leaning on the bad side. But small independently owned fish stores can be an amazing resourse, particuarly to someone starting out,
Seachem prime is my favorite dechlorinator due to how concentrated it is – it’s lasts longer than others. Also, since it can render nitrites and heavy metals harmless, it is useful in other emergencies. If you find another dechlorinator that works better, for a reasonable price and is commonly available for beginners, I’ll gladly swap out my recommendation.
But I do thank you for sharing your advice.
Hey Li, I read your comments about letting water sit or boiling it. You must have a very small aquarium if that’s what you’re doing. I have a 250 gallon Marine tank and when I do my water changes I’m removing a lot of water. It’s NOT feasible to boil 100 or 150 gallons of water. I really don’t think you know what you’re talking about!
Hi Ian, it’s Steve again. Hope you are well since we haven’t talked in a while. My tank is doing great, fish are healthy and have not lost any. Water chemistry continues to be good with no problems. Tank water cleared up with the use of the 50 and 100 micron filter pads although it still looks a little cloudy to me.
I’m wondering if the Bio Max that’s used in the Fluval filters is putting some particles into the water? I’ve been thinking of using Bio Balls instead since they are plastic. I would appreciate your thoughts about that, thanks.
Hi again Steve,
I’m glad to hear your tank water has improved in clarity. Did you rinse your ceramic media before adding it to the tank? This will get rid of most of the lose dust and rubble that comes from the ceramic grinding against each other during manufacture and transport. I would be concerned if your biomedia is dissolving at such a rate it is putting noticable debris in the water.
I use sera siporax for my media and have not had an issue with clouding. I have also seen other tanks achieve crystal clear water while using cheap ceramic rings, so I don’t feel there is a need to swap over to a plastic biomedia, which IMO is inferior in terms of surface area for beneficial bacteria to live.
Also as an aside, how does the water look with different lighting? It’s possible your lights are making the water look cloudier than it is?
Hi Ian, thanks for your reply. I did rinse the bio media thoroughly before placing it in the filters. I asked the question because when I rinse the mechanical filtration at times I notice small white particles on the carbon bags that are under the bio media. As for the lighting I also thought that may be the cause but I
don’t believe it is because the water still looks slightly cloudy with it off.
Hi Ian, hope you’re having a great weekend. So guess what? I took 5 gallons of tank water and put it in a bucket. Then I rinsed the bio media from both the HOB Fluval 70’s in that bucket then put the bio media back in the filters. There was some small white particles that were in the water. Today the tank is clear and looks like it should. Tomorrow I’m going to do the same thing with the bio media in the Fluval canister. Even though I’m not a beginner as you know I’m still learning every day 🤔. Stay well and as always thanks for your help.
Hi Steve!
I’m doing well, thanks. I hope you are enjoying your weekend too!
That’s very interesting regarding the particles. Thanks for the update, I’m sure someone else will have the same “problem” in the future and I can now suggest this as a cause! Thanks for sharing 🙂
Hi Ian,
I don’t see a lot of mention about “jump starting a tank” with Nitrifying bacteria. I have a 75 gallon Cichlid tank with 12 small Cichlids in it. I’m running a Fluval G6 and right before plugging in the pump, I put a whole bottle of One and Only Live Nitrifying Bacteria by Dr Tim. With 12 Ciclids and 2 Cory Cats, so far so good. Everyone is active, vibrant and eating. I monitor every day and only have trace NH3. I have been placing a packet of Marineland Bio-Spira bacteria in the tank every other day…right at the filter intake so it goes directly to the biomedia. I am a week into the cycle, no fish loss and clear water. I still have my UV filter off but my bio-filter and 2 power heads and multiple air stone decorations are going 24/7. Temp, GH, KH, pH are in normal range for Cichlids. I have done 2 15% water changes and using Prime on water change water and when I detect NH3. I check twice a day. My EC (electrical conductivity on the filter is reading ~900 which is high). Not sure why.
Any other comments?
Hi Michael,
You are definitely braver than me doing a fish-in cycle with that many fish.
The reason why I don’t really cover “jump starting” with bottled bacteria because it can be hit and miss as to whether or not it actually speeds up a cycle. I have some tanks cycle in under two weeks with it added as well as the opposite. I have also seen tanks cycle in under two weeks without it.
You have not listed your nitrite or nitrate readings. Nitrite is as dangerous as ammonia during cycling. Are you monitoring this too?
Hello Ian, Thank you , thank you, thank you! The filter pads came sooner than I expected as I have an Amazon fulfillment center near my home. I put the pads in all 3 filters on Thursday and did a 25% water change. By Saturday the tank looked great. I did change the pads Saturday in both the Fluval HOB 70’s as they were dirty and put clean ones in. I’m going to order some 50 micron pads just to see if they have more of an effect. As always thanks for your help, it’s been a pleasure talking with you. 😀
Hi Steve,
I’m a little jealous of how close you are to an Amazon fulfillment center – my orders never come that quick.
That’s awesome. I’m so happy to hear it. Depending on how gunked up the pads are, you may be able to rinse them in fresh water to extend their use – since you are not worrying about beneficial bacteria in these pads, you can be pretty rough with your cleaning.
Here’s to your new crystal clear aquarium. Wishing you all the best in your future fishkeeping endeavors 🙂
Thank you for all the great info! I have been following your steps after I made a mistake and messed my cycle up from setting up a new Hob filter and not Seeding it with bacteria from my old one. My readings today was 0ppm ammonia 0.25ppm nitrite and 0.5 nitrate. Do you beleave I am on the road to a cycled tank???
Hi Zach,
It depends, if it’s been over a week then sure. If this is your first day then something is amiss.
Hello Ian, I have looked at that site before and I have no doubt you are correct that there are small particles floating in the tank. The filter pads I purchased may not be the correct ones since the packaging didn’t say how many microns they are. I have ordered 100 micron pads from Amazon, just waiting for them. As always I appreciate your comments. I’m going to wait until I get the new pads, put them in and let the filters run for a couple of days before we talk again. Best wishes as always.
Hi Ian, I completed my gravel vac and water change, had quite a bit of waste in the gravel. Waited 1 day and tested the water, chemistry is good. The water still looks a bit cloudy and I’m wondering why. As you said there’s plenty of filtration so I would have expected it to be crystal clear. I’m still waiting for that to happen. If you have any thoughts about that I would like to hear what you think.
Hi Steve,
It’s possible that the pieces of debris that are floating around your water are so small, they are actually slipping through the gaps in your filter pads. This is an easy fix. Simply grab a super fine filter pad (50-100 Micron) like this one and place it after your coarser filter pad. It will trap the tiny particles that slip through and will return your water to a crystal clear state – it beats using chemical water clarifiers.
Also, if the bottom of your tank was particularly foul and kicked up a lot of gunk, you might need to give your filter pads a rinse in fresh water, to remove the excess sludge that has built up.
Hello Ian, thanks for the advice I didn’t even think about that. I’m going to pick up the filter pads today and I’ll reach out to you after the weekend and let you know the results. As always your comments are greatly appreciated.
I hope it all works out for you. Have a great weekend!
Hi Ian, hope you had a great weekend! I think the tank looks a bit better today. This morning I removed the carbon from both the HOB Fluval 70’s and added more microfiber in its place since there is carbon in the Fluval 406 canister which I also put microfiber pads in on Friday. Maybe it’s going to take some time for the water to completely clear. I would like to send you a picture of the tank, maybe you may see something I’m not. Let me know if that’s possible and how to do that. Once again thanks and best wishes.
Hi Steve,
Thanks, I spent some much needed downtime with my fish!
Unfortunately I do not have the ability to receive photos through comments.
However, it will take some time for the filters to trap all the micro particles as long as you bought the right stuff, it will eventually all be trapped. The remaining gunk will settle on the bottom of your tank, ready for it to be siphoned away the next time you gravel vac.
The only other thing it could be is floating algae or bacteria, which will multiply in the tank but that’s a whole other ball game. From what you are saying, it sounds like small floating particles. Algae and bacteria have a much different look. You can see pictures of these in the cloudy aquarium water guide.
Hello, love this site, I now understand the cycling process!
However, please can I ask some advice?
I’ve had my 40l tropical tank for a few years but have never been successful in keeping fish alive in it 😔 I decided that I have probably never properly cycled my tank and so thought I would start again and get it right this time. Twice the heater has overheated the tank and so I made the decision to get rid of it and go cold water with goldfish. I had kept the tank and filter running since the last of my fish died. The pet shop convinced me to get ‘temperate fish’ and so I came home with 4 platies and 2 snails. Then I did my research (yes I know now that I should have done this before getting the fish and am kicking myself that I could have cycled so easily with just food!).
I took your advice and got the testing kit you suggested. The fish were put in the tank 2 days ago and I have completed small water changes twice daily since. So I tested this evening (before my evening water change) and results were;
Ammonia 0
Nitrites 0
Nitrates 20
pH 8.2
Does this mean my tank is in fact cycled?
Also how do I bring the pH down?
Many thanks in anticipation of a response, any advice would be gratefully received.
Hi Laura,
Welcome back to the hobby! I hope you find more success this time round.
I would be hesitant to say that your tank has cycled after just two days. I would continue testing each day and perform water changes if your test results return a reading, for the next week.
As for pH, you can lower pH naturally with indian almond leaves or peat moss. Alternatively, you can use RO water however this will require you to remineralize it before adding it to your tank.
I set up a 75 gal fresh water tank late August. I’m cycling with fish in the tank. I have been testing my water every 2 or 3 days. I have never seen an increase in Ammonia, Nitrites or Nitrates. I was doing partial water changes but have stopped. Water chemistry continues to be good. My tank water has been some what cloudy and has not cleared as of yet. The fish are healthy and eating well. Please help if you can.
Hi Steve,
I would double check your test kit has not expired and isn’t faulty – ammonia won’t take long to build up to measurable levels.
If there is no ammonia or nitrites but nitrates, then your tank has cycled. Given that it has been over a month since you set up, this is another possibility.
Hi Ian, thanks for your reply. I checked my test kit and it is good until 2020. I’m using Tetra test strips and have also had the water tested at the local Pet Smart. I checked my water again today. No Ammonia, Nitrites or Nitrate. I’m really at a loss because this is not my first Aquarium. I had a 250 gallon Marine tank for several years and never had issues. I’m ready to go crazy.
Hi Steve,
Given you are not a beginner, I’m actually leaning towards thinking your tank is cycled and that something is depleting the nitrates. I mean, if there is one thing fish are good at, it’s producing ammonia.
No need to go crazy just yet. If you want peace of mind, I’d take a photo of your tank, write up your weekly ritual and list the equipment connected to your tank and post it to an online aquarium forum – it’s likely someone else has experienced the exact same problem as you before.
Hello again Ian, I appreciate your insight and comments. I’m not very tech savvy when it comes to posting on a forum. I am running 2 HOB Fluval 70’s as well as a Fluval 406 Canister filter. I believe your assessment that my tank has cycled is correct. Today I’m going to gravel vac which I haven’t done since I set up the tank
and perform a water change. I figure the worst that can happen is the cycle process starts over but I don’t believe it will. I will let you know in a few days the results, wish me luck!
Hi again Steve,
Hey, no need to doubt your abilities. If you can comment here, you are more than tech savvy enough to post on a forum!
Given that the vast majority of beneficial bacteria hides in your filter media, vacuuming the gravel and doing a water change shouldn’t have an effect if your tank is already cycled.
Also, that is a lot of filtration for a tank your size. Most would stop at just one of those filters. Not that this is a bad thing at all, more is always better.
I’ll be very interested to hear your results after performing maintenance.
Good luck!
Hello Ian, yes I definitely have a lot of filtration on my tank. I think it comes from when I had the 250 gallon marine tank for 15 years, it also had a lot of filtration. So I did a gravel vac and 75% water change. I tested the water this morning and chemistry is good, tank water looks much better. There was a lot of waste in the gravel that came out. I think I’m on the path finally and can enjoy the hobby again. I appreciate all your comments and help. It’s been a pleasure chatting with you, best wishes.
Hi everyone,
I am new to the aquatic community and I have a 50g tank. I set up the tank 2 days ago and got eager and put some fish inside already. I currently have:
1 plecostomus
1 catfish
1 green tiger barb
2 stripped tiger barb
2 angel fish
2 snails (not mystery snails)
2 black cichlids (temporary)
When I bought everything from PetSmart, the lady failed to mention the nitrogen cycle, so I just put all of the fish in the tank with the water. Today, the tank was cloudy and according to the internet, that’s a bacteria blood, which is good I guess?
Anyway, I went to Petco this time and they were way more helpful.
I just would like to verify if what she said was correct.
The girl told me to remove 50% of the water and replace it with Seachem Prime treated water. Then test it with the API kit.
I just did a test now and the results are:
0.5ppm Ammonia
0.25ppm Nitrites
5ppm Nitrates
Where should I go from here? I only have a 5g bucket to treat and replace the water, so I’m not sure how to dose the Prime since it’s 5ml/50gallons. I have been using a bacteria supplement as well on the first day I received the tank. Should I continue to use the bacteria supplement for every water change?
Thanks everyone!
Hi Vanessa,
You can can work your way through the steps listed in this guide.
A 50% water change is going to take you 5 trips with that bucket. Once you get to tanks this size, I suggest using a water changer instead of siphoning into a bucket – it’s going to save you a lot of time and effort, depending on how far your tank is from the nearest water source.
On the prime question, .05 ml. use a measuring pipette, it will make it easier to precisely dose. Don’t worry if you add slightly more, an overdose shoudln’t harm your fish.
As for the bacterial supplement, there is debate as to their effectiveness. However, there is no reason not to continue with it. If it has been properly stored and within it’s expiry date, it won’t harm your tank.
Your tank is too small for the pleco! Pleco should be put in minimum 79 gallons for one. And they need to be several plecos, not only one, or it’s not a good life for a fish that likes to be in bank to be alone! So it’s not a wonder that you have nitrite & nitrate problems. For the other fishes, I don’t know, but try to get info, because for the pleco, you haven’t been given good advice.
Buy a bigger tank, or give your pleco. Plecos are not good fish to keep in a tank, they shouldn’t been bought, they require too many gallons and family members.
Doing 75% water change is too much, it’s very stressful for fish. It should be done in my opinion only if there’s a big problem with the quality of the water. Most of the bacteria are in the filter, that’s right, but you lower the number of bacteria when you do a water change, they are not all in the filter, there are also bacteria in your soil, and on every surface they can colonize, but a large part is often in the soil.
Hello I am hoping you can help me. I’m at a loss. I just recently started my first tank. We had them when I was little but I was never responsible for them and back then no novice really knew anything about the nitrogen cycle. I started researching early and went to our local aquarium store. On August 10 I set up a 15 gallon freshwater tank using Aqua Life Complete water conditioner. They also told me to get to cheap hardy fish to start my cycle. They also had me add Aqua life activate along with my 2 Glo Fish tetras. There are also 3 live plants.On August 16 more Activate was added. Then I tested using API master test kit on the 22nd. pH was 7.6, HRpH 7.4, Ammonia .5ppm, no No2 or No3. My friend who keeps fish told me to do a 50% water change at this point. I also added a bubble wall. On the 21st I did have some bacterial bloom which cleared up pretty quickly. Tested on the 24th and got these differences Ammonia <.25ppm still no Nitrites and now 5.0 nitrates. Exact same thing on the 28th. I'll admit at this point with my fish continuing to seem healthy and happy and my numbers the exact same, I added 2 more Glo fish Tetras on September 2. Continue testing, some more water changes sprinkled in there and still the exact same numbers. On September 7 I took sample to the Aquarium store and had them test and they got the same numbers and said it of course had no cycled yet so add some more Activate which I did. All 4 fish continue to be healthy and seem active and happy. I had run across your blog
last week and ordered some Seachem Prime to try your method. Yesterday I tested and got all the same numbers. I have also started seeing some visible algae on the decorations so my friend recommend I clean it up since I have no algae helpers yet. So I cleaned some noticeable areas and did a 30% water change using the Prime for the first time, since I was about 1 in low on water from all the testing. I got busy cleaning the house and forgot to empty the test tubes immediately and came back to the about 6 hours later. The ammonia was definitely yellow no more doubt that it had any green tint. Not being a chemist I don't know if that would just happen to any ammonia reading OR if it was a more accurate reading. 24 hours later I just tested and got the same numbers but it does appear that the Nitrate reading comes quicker even though it's only 5.0. I've yet to have any Nitrite reading. Sorry so long winded but I wanted you to be able to have a full picture.
Hi Heather,
Unfortunately, cycling is something that takes weeks and to get a true picture of what is happening you should write down each days results and compare them. If your nitrates are going up, then they have to be coming from somewhere, and it could be that your tank is well on it’s way to being cycled.
Also, I wouldn’t trust any test reading that had been left to sit for 6 hours.
If Aqualife Activate acts similar to prime then it is possible that your test kit is giving a false positive for ammonia, including ammonium (harmless) in the total. As far as I know, Seachem is the only test kit manufacture that tests ammonium and ammonia separately.
Alternatively, you can use a free ammonia calculator like this one (NH3 is ammonium, NH4 is Ammonia) to see what is happening in your tank, However, you will need to know your tank temperature, pH and Salinity in addition to your ammonia measurement. While most saltwater tanks will know their salinity, most freshwater tanks won’t and you’ll need a device to measure this.
The alternative is to leave it a few days, see what happens to your nitrate levels. If you think your tank is cycled, you can skip the prime for 48 hours and re-test.
Thank you. I will get a Sea chem ammonia test kit. Because right now none of my numbers are changing. I know it can be a long process but as you can see I’ve never had a spike of numbers to even think anything is happening. I just feel at a loss. And nothing I read seems to match what I’ve seen happening.
If you have fish in your tank, then ammonia, nitrite or nitrate levels should all be increasing. Ammonia is given off when you feed your fish, when they poop etc, it’s unavoidable and at the very least you should be seeing a change in the ammonia reading after a few days.
That’s what I keep reading but here I am a month into it and nothing’s changed. I test every day. And it’s always the same.
Ok I’ve been dosing with Prime. I tested today and there was definitely no ammonia. Still never had any nitrites. Nitrate color looked paler orange today too. pH is 7.6 and HRpH is 7.4. Tank temp is 80F. Should I just keep dosing with Prime?
Hi Heather,
If you believe there is no ammonia, and no nitrites but your nitrate levels keep increasing, then your cycle is done.
Prime wears off 24-48 hours after each dose (assuming you dosed correctly as per volume of your tank) If you wanted, you can keep testing multiple times through this window and past it, to make sure everything looks okay.
Alternatively, keep dosing and monitor your nitrate levels. If they continue to rise but your ammonia and nitrate stay at zero then you can be confident your tank has been cycled.
Hi
I’m doing fish in cycling with prime as per your instructions, should I still normal weekly water changes through the process?
Thanks
Amy
Hi Amy,
If you find yourself doing a water change before the week is out, there should be no need to perform a weekly water change.
I have a betta in a 5 gallon. First fish ever. Now I know I put him in prematurely, but I am reading as much as I can and testing daily to keep him healthy. I have been getting ammonia readings 0.5ppm on once daily testing (no nitrites or nitrates yet) and have been doing a 30% water change daily (with added water conditioner). Is that too much or too little? I’m wondering since the bacteria need ammonia as a food source and I’m always removing it, how can they really take hold? I did add the recommended bacteria supplement on initial set up.
Hi Amy,
As long as there is ammonia in the tank, beneficial bacteria will eventually begin to establish. Unfortunately, this can be a very slow process. My last tank took me almost a month to completely cycle. Is the 0.5 ppm measurement before or after you are performing the water changes?
Before the water change. I test, then change 30% if I am seeing ammonia. I have been waiting 24 hrs to test again.
It might be worth testing after the water change, to make sure that the levels are not dropping down to unreadable levels. The results you read before the water change might be due to it building up over the day.
I do not know about the cycle and till I buy 20 gallons tank, fish and substrate. I have over 10 fish die gradually. I test my water in pet store, they finally all come out good after 6 weeks but eventually all fish are dead except 2 coral cat fish. I am not using that tank because I want to start over again. now I use a old turtle tank for remaining 1 catfish. it is 10 gallon, I restart the cycle. in beginning the ammonia is very high, then I do 100% water change, it is 4 days ago, now the ammonia around 1ppm. no trace nitrite but about 40ppm nitrate. the tank just set up about a week. should I do another water change again? does my cycle done? I put some water and decoration from a exist dirty 2 liter fish tank with fish inside and add to this new tank. I read on line and says it will help to speed up the cycle.
Hi John,
If you have performed a 100% water change during cycling, then it’s possible that you have removed the all the nutrients needed for your beneficial bacteria to grow, stalling or even restarting the cycle. If that’s the case, you are back to square one and will have to try again.
Thanks, my daughter is planning on taking a fish up to college with her in a few weeks. She decided on getting a juvenile pictus with her. She set up a new tank with a sand substrate since he didn’t seem to like the gravel in the community tank. He loves the sand but she read you should totally replace it every two weeks but wouldn’t that slow down the cycling of this new tank (we added lots of yucky filter juice and quick start to try to speed up this new tank). She tests constantly, and is doing frequent water changes with Prime and Stability. He seems to be happy.
Two questions…the pet store person grabbed the little guy with a net and he was stuck. It looks like he has a fin fracture on one if his dorsal radials. It turned white and he got a little white bump on the fin but everything else looks fine and nothing is spreading. Do you need to do anything to treat it? He is swimming fine.
Second, should she take Sigmund home on Thanksgiving break? It’s only 4 days. I doubt the water temp will drop below 70 even if the RA turns of the heater. I figured she could put one of those vacation bricks in. She thinks it would be better to take him home (3 hour trip). What do you think?
Hi Susan,
Most of the beneficial bacteria lives in your filter. Only a small is found inside the tank itself. If your filter is rated for your tank, properly cycled and your tank isn’t overstocked, swapping out the substrate shouldn’t cause the tank to crash.
Even so, two weeks for swapping over a substrate sounds both excessive and hard work. Most fish keepers I know stir the sand and use a gravel vac to keep the surface clean. Breaking off a prong from a plastic fork and taping it to the end of the gravel tube will allow you to both stir the sand bed while whipping up any gunk sticking on top without sucking up much of the sand.
If it’s a physical injury, all you can do is leave it to repair naturally, paying extra attention to keeping the tank very clean and water parameters normal – there isn’t such a thing as casts for broken fins.
Most well fed fish can happily survive a week and often more without food – in the wild your fish wouldn’t have a regular meal time, and may only come across a meal every few days. Best way to test this is to do a trial run, skip feeding him for 4 days and watch closely to how it fairs. If you plan to go down the vacation block route, do the same – many users report that the block fouled up their water, killing their fish.
I’d still recommend buying an aquarium heater. It’s not the temperature itself that kills fish, but rather the rapid temperature change – the temperature in a small tank can drop and raise quickly, causing stress.
I use products with bacteria in them to get a head start. Works pretty well for me. I also use a product that helps protect fish from nitrite spikes. It helped save my fish when my bacteria colonies died and I had to rebuild them. Plants can also be a good way to keep ammonia, nitrite and nitrate down. From what I’ve read floating plants and those little moss balls both work pretty well. Floating plants can get CO2 directly from the air instead of the water which helps them clean up the water more.
These days I almost never change the water in my main tank due to a large number of plants. I monitor the water closely though.
Hi Katherine,
Thanks for sharing your experience! Sounds like you have a pretty advanced setup – especially if you are able to go weeks without water changes.
Bacteria in bottles or tablets are totally useless. Proving that it makes the cycle shorter has never been done. It’s only to make you give the money. It’s a waste of your money. If you don’t believe me, try to find researches on the duration of the cycle with the all dead bottled bacteria, and without.
I’m currently on my 3rd week of a fish in cycle.
I re-homed 4 danios from a friend who no longer wanted them, and at this point knew nothing about ‘cycling’ a fish tank, or really much about fish, except that new tap water should be de-chlorinated.
The fish lived happily for a little while, then 1 got poorly and died, then a 2nd, and then sadly a 3rd.
At this point I knew something was up and then started to research about coldwater fish, and low and behold found out about cycling.
I basically started again with the last remaining danio. I bought a new tank, filter etc… and started the cycling process.
I have a quick question…. My ammonia levels have lowered over the 3 weeks (currently 0.25ppm), however the nitites and Nitrates are really high, above the acceptable level.
Will regular water changes keep this under control, aswell as allowing the beneficial bacteria to establish?
I add aquarium salts, and some good bacteria, but it seems to be a slow process, and just worry for my last remaining fish.
Any help / reassurance appreciated.
Hi Amy,
Unfortunately cycling your tank is never instant it can take weeks or even months – patience is key. I know this can be hard when you have fish dying before your eyes but hang in there!
It sounds like you are nearing the end of the second stage of the nitrogen cycle. Here is a chart from the last time I cycled an aquarium. As you can see, the nitrites build up before slowly dropping in number as nitrates begin to appear. You are nearly there! To get a greater idea of where you are in the cycle, perform daily checks with your aquarium test kit for ammonia, nitrates and nitrites.
Performing water changes will help keep your nitrites and nitrates down. Just be mindful that don’t want to remove all the nitrites, as your colony of bacteria needs this as a food source. Make sure you test closely.
You got this!
Wish I’d seen this article before I started. Into week five and nitrites just appearing but was ill informed at pet store. Started with 4 fish ( buy 3, get one free). Now have 2. Will know better next time.
Hi Jomardeuse,
Thanks for sharing your experience! I’m sad to say that this is not uncommon. That’s why finding a good local fish store, with knowledgeable staff is essential in this hobby – for a beginner, keeping fish is more complicated than it first appears.