You bought your new aquarium, filled it with water. The next step is adding fish, right?
If you add your fish now, they will soon be dead.
Before you add any fish to your aquarium, there is one important thing you must do:
To beginners, the nitrogen cycle is considered the most confusing part about owning an aquarium.
But don’t worry – it doesn’t have to be this way.
I am going to show you how to cycle your aquarium the right way, with fishless cycling – it’s much easier than it looks.
What is the nitrogen cycle and why is it so important?
You may have heard the terms biological cycle, nitrification process or break-in cycle. Don’t get confused, these all refer to the same thing I cover in this guide – the nitrogen cycle.
Before I show you how to perform a cycle, it’s important that you know what is going on behind the scenes.
Imagine swimming in a pool surrounded by your own pee and poop.
Sounds horrible, right?
Your fish feel the same.
Unfortunately, there is no such thing as a toilet for fish. So, your fish will poop and pee in the same water they swim in. That’s like you pooping in your bedroom!
As your fish’s pee, poop and other waste breaks down, it releases ammonia into the water. Ammonia is a toxic substance that will kill your fish. Death by poop? No thank you!
Luckily, nature is on your side. The nitrogen cycle prevents your fish from meeting this horrible end.
In this natural three-stage process, you encourage beneficial bacteria (good bacteria) to become established in your tank and filter, keeping your fish safe from ammonia.
Let’s take a closer look at the nitrogen cycle…
The nitrogen cycle process
See this diagram? This is the nitrogen cycle in a nutshell. Let’s break it down.
Stage 1: Ammonia (Harmful)
It begins with waste. Poop, pee, uneaten fish food and rotting plants all give off ammonia as they break down.
Ammonia will continue to build up in your tank, reaching deadly levels. That is, until a beneficial bacteria that eats it begins to form. These bacteria naturally appear in your tank on their own and once they grow in number, they can eat ammonia as quickly as it appears.
You know these bacteria are present in your aquarium when your ammonia levels begin to decline, typically after the first week. And when that happens, you know that you are entering the second stage of the nitrogen cycle…
Stage 2: Nitrites (Harmful)
Just like ammonia, nitrites are highly toxic to your fish.
But not to worry because as your nitrite levels rise, a second bacteria appears in your aquarium. It’s favorite food? Nitrites
Once this good bacteria grows in number, it can eat nitrites as quickly as they are produced.
You know this bacteria is present in your aquarium when you see your nitrite levels begin to fall. When this happens, you have entered the final stage of the nitrogen cycle.
Stage 3: Nitrates (Harmless)
Nitrates are the final product of the nitrogen cycle. And, they are relatively harmless to your aquarium, at least in small amounts.
But as nitrates build up, they can become toxic to your fish. Fortunately, nitrates can be lowered back to harmless levels by performing a water change. In fact, this is one of the reasons why you should be performing regular water changes on your aquarium.
And, that’s really all there is to the nitrogen cycle!
That wasn’t so hard, was it?
When you cycle your aquarium, you are simply forcing your tank to undergo the nitrogen cycle.
The reason you need to cycle your aquarium is so that these two beneficial bacteria can grow to the point that they can eat the harmful ammonia and nitrites as quickly as they produced.
At this point, you can consider your aquarium effectively cycled.
It’s important to understand that the nitrogen cycle is continuous. While you can’t see it, this cycle is constantly happening in your aquarium, keeping your fish safe from harm.
What happens if you don’t cycle your aquarium?
The nitrogen cycle is a funny thing in that it’s going to happen whether you want it to or not.
If you add your fish to an uncycled aquarium, the food and poop breaking down is going to introduce ammonia, which kick-starts the cycling process.
In fact, this is the very idea behind fish-in cycling – a method of cycling an aquarium that is best left to the experts.
Just one problem…
You see, your fish are in the tank while toxic ammonia and nitrite levels rise. To say these things are dangerous to your fish is an understatement.
This toxic environment is incredibly harsh on your fish – most fish cannot survive this cycle, and the ones that do are more susceptible to disease and don’t live as long.
So while a tank may cycle itself without any effort on your part, there is no guarantee that your brand new fish will survive it.
Unfortunately, if you have already bought fish to go with your new tank, a fish-in cycle maybe your only option.
If you are in this unfortunate position, don’t panic. I created a fish-in cycling guide that will give your fish the best chance of survival.
How long does it take to cycle your aquarium?
The other day I was stocking up on supplies at a major pet store. In the next aisle, I overheard a conversation between an employee and shopper who wanted to buy a pet fish.
I won’t bore you with the details, but the employee was working hard to pitch this shopper a new tank – claiming that modern tanks only take one day to cycle. After this 24-hour period, it’s safe for fish.
Those of you with a bit of experience will see right through this lie.
But for those of you who are new to the hobby, cycling your aquarium is going to take a lot longer than that!
Depending on who you ask, cycling your aquarium can take anywhere from 2 weeks to 2 months.
The best answer:
It will be finished when it’s finished.
If you are lucky, your cycle might be short. But don’t be upset if it takes longer – we’ve all been there before and it sucks!
The problem is that the bacteria you introduce in the cycle grow very slowly. And all you can do is wait.
It is for this reason that you should cycle your aquarium before you buy your fish. Don’t add them to your aquarium before it has cycled.
Remember… Cycling isn’t an instant process. But you have to do it if you are planning on keeping happy and healthy fish.
But don’t stress – I’ll cover some tricks that you can use to speed up the cycling timeline later in this guide.
If you do not have the patience to cycle your aquarium, then fish are not the right pet for you.
How to cycle your aquarium the easy way
There are two ways to cycle your aquarium:
Fishless cycle – A beginner-friendly and harmless method to cycle your aquarium
Fish-in cycling – Recommended only for experts because this method could potentially kill your fish
As you probably guessed, this guide covers cycling a tank without risking the lives of fish. And, it is the most popular and common technique used to cycle aquariums.
Note: There are many ways to perform a fishless cycle. This beginner-friendly method, if followed step-by-step, is almost foolproof.
What do you need to perform a fishless cycle?
When it comes to cycling your aquarium, you only need three products…
1. An aquarium test kit
The nitrogen cycle is an invisible process. The only way to truly understand what is happening inside your tank is to test for it. And, the most popular way to do that is with an aquarium test kit.
I recommend buying a master test kit like the one above because it contains every test that you need to cycle your aquarium at one low cost.
Learn how a test kit works. Check out FishLab’s aquarium test kit guide.
Instead of waiting for waste to break down into ammonia, add it directly. This will make it easier to keep ammonia levels constant.
Important: Use 100% pure ammonia. Many household ammonias contain scents and additives, and this is going to kill your cycle before you even start. Stick to pure ammonia, like the one above.
Are you using tap water to fill your aquarium? Be aware that it contains chloramine and chlorine, two chemicals that kill beneficial bacteria in your tank.
Fear not! Adding a good water conditioner to your aquarium will dechlorinate your water, making it safe for the beneficial bacteria (and fish when you finally add them).
Use this whenever you add tap water to your aquarium.
Have these on hand? Good. You are now going to learn how to cycle your aquarium in 6 simple steps.
FishLab’s 6-step cycle method
Cycling your aquarium is easy…
As long as you carefully follow the instructions!
So, slow down and make sure you understand each step before moving to the next. If you don’t, you risk ruining the cycle. And if that happens, you will have to start over.
Step 1. Set up your aquarium
You know all that equipment you got with your aquarium? Well, you need to set all that up.
Why do you need your tank fully set up?
Well, beneficial bacteria needs a surface to cling to, namely your substrate and filter media. In fact, most of the bacteria will call your filter home.
Once your tank is set up, you want to keep any electrical equipment, such as heaters, bubblers and filters, switched on throughout the cycling process. Doing so encourages the beneficial bacteria to grow and may even make your tank cycle faster.
Note: Beneficial bacterial prefer temperature between 65-85 degrees Fahrenheit. Growth is slower outside of this temperature range – which can cause your cycle to take longer to complete. Check your water temperature with an accurate aquarium thermometer.
Step 1 Summary
- Set up your aquarium
- Turn on all electrical equipment
Step 2: Check your pH
This is perhaps one of the most commonly missed steps when it comes to cycling your tank – and a common cause of failed cycles.
You see, the cycling process can slow down or even stop if the pH level of your water drops below 7.
Since the master test kit includes a pH test, it would be silly not to use it now.
So, check the water you added to your aquarium with your test kit. If it’s below 7, you need to raise your pH before moving to the next step.
Good news! This won’t be a problem for most of you because the majority of water supplies across the United States test at a pH that is greater than 7.
Even so, you want to continue performing pH tests throughout the cycling process. You see, the beneficial bacteria in your tank give off acids that lower the water pH over time.
If you notice that your pH levels drop under 7, a simple 20% water change is all that’s needed to raise the pH and get the cycle going again.
So, make sure you test your pH regularly and adjust it if needed.
Step 2 Summary
- Test the pH of your water
- Adjust when lower than 7 pH
Step 3: Add your ammonia
In a brand new tank, there won’t be any waste, meaning nothing to break down into ammonia. So, we must add it ourselves.
Simply take your Fritz Ammonia and read the instructions.
At the time of writing this, one level teaspoon of Fritz Ammonia per 100 gallons of water will give you an ammonia level of 4 parts per million (ppm).
You need to know how much water is in your aquarium in order to add the correct amount of ammonia. Use FishLab’s gallon calculator if you are unsure of just how much water your tank holds.
So, measure out your ammonia…
Fish tanks less than 40 gallons: Aim for 2 ppm
Fish tanks more than 40 gallons: Aim for 4 ppm
While you can steal the measuring spoons from your kitchen, I recommend having a dedicated set of measuring tools for your aquarium.
You now want to make sure that you have added the correct amount of ammonia. And to do this you are going to use your aquarium test kit, which will give you a result in ppm
But before you do that, you want to let the ammonia sit for an hour, so that it evenly distributes throughout the water. Next, measure the ammonia levels using the ammonia test from your master test kit – Make sure you follow the instructions provided by the test kit for accurate results.
If your ammonia readings are less than the above levels, add more ammonia and re-test.
If your ammonia levels are higher, perform a water change. Doing so will swap out your high-ammonia water with ammonia-free water, lowering the levels.
Record the amount of ammonia that you added. You will need that information in the rest of the steps.
Ammonia levels higher than 5 ppm can actually slow down the cycling process.
Now, the next part will test your patience. Check your ammonia levels each day with the test kit. This is as much as you can do for now. You are waiting for your ammonia levels to drop.
This typically takes a week. Once a week has passed, it’s time to move onto the next step.
See you next week!
Step 3 Summary
- Add ammonia to your aquarium
- Daily testing to monitor ammonia levels
- Don’t forget to test the pH every few days
Step 4: The ammonia eating bacteria appears
After a week has passed, it’s time to test for nitrites. So, grab your nitrite test kit and check the levels.
If your test comes back positive, congratulations – your cycle has officially started!
Now, it’s important to remember that this bacteria feeds on ammonia. And the only thing adding ammonia to this aquarium is you. If your ammonia levels reach zero, this bacteria will starve, and you will have to start your cycle all over again.
So, we are going to give this bacteria a little more food. Add half the amount of ammonia that you added on day one, but make sure that your ammonia levels remain under 5 ppm.
Now what you want to do is monitor your nitrites, testing daily. You should notice the nitrite levels continue to rise. Once you see your nitrite levels start to drop, it’s time to move onto the next step.
See you again in a few days!
Step 4 Summary
- Once nitrites are detected, add a half dose of ammonia
- Ensure ammonia levels are less than 5 ppm (but greater than 0 ppm)
- Daily testing of ammonia and nitrite levels
- Don’t forget to test the pH every few days
Step 5: The nitrite eating bacteria appears
To confirm that the nitrite drop is due to the beneficial bacteria, use your test kit to check for nitrates. If they are present, you are now in the final stage of cycling your tank.
Now, we still want to make sure that the bacteria has enough food to eat. So add a half dose of ammonia as needed, each day if you have too, to keep the levels above 1 ppm.
Continue testing. When you can add a half dose of ammonia and both your ammonia and nitrite levels read zero 24 hours later, your nitrogen cycle is complete.
Woo! Home stretch… Just one more step to make it official!
Step 5 Summary
- Test to confirm nitrates
- Daily testing of ammonia and nitrite levels
- Add half doses of ammonia every few days
- When both ammonia and nitrites show <0.2 ppm, swap to daily dosing
- Test until both ammonia and nitrites read zero 24 hours after dosing
- Don’t forget to test the pH every few days
Step 6: The Final Test
You are so close. You just want to make sure that your tank is fully cycled. To do that, one last test is in order…
Once your ammonia and nitrite levels reach zero, add a full dose of Fritz Ammonia, the same amount that you added on day one. Now, will need to wait one last time…
Check back in 24 hours. Test your ammonia and nitrite levels. If both read zero….
Your patience has paid off, and your tank is now fully cycled.
If you record your test kit readings each day, you will have a clear understanding of the nitrogen cycle.
This chart is from the last time I cycled my tank:
It took me 28 days to cycle the aquarium.
You see a distinct rise and fall of ammonia and nitrites as the beneficial bacteria become established in the tank. You can also see how nitrates drop at each water change.
I highly recommend recording the results of your test kits each day. Not only will it give you a better understanding of what is happening in your tank, but you can also use the results for troubleshooting.
Now that your tank is cycled, the bacteria colonies are large enough to remove ammonia and nitrites as quickly as they are produced…This nasty stuff won’t be harming your fish anytime soon!
But before you add your fish, you want to perform a water change to remove those built up nitrates.
Speaking of which… You should add your fish to your tank now. If you don’t plan on adding fish just yet, keep dosing the tank with ammonia daily. This will ensure that the beneficial bacteria don’t starve. If the bacteria starve and dye, you are going to have to cycle your fish-tank all over again.
It might have felt like a lot of effort, but your hard work will be rewarded once you see just how healthy and happy your fish are. And, it’s all thanks to your newly cycled tank!
Phew, you did it! You should be proud of yourself. Your patience has paid off, and your tank is now cycled.
By cycling your aquarium, you give your fish the best possible chance to live a happy and healthy life.
Just remember that once started, the nitrogen cycle consistently runs in the background of your aquarium.
But you are not home free just yet.
You still need to continuously monitor your ammonia and nitrite levels to ensure that something hasn’t gone wrong. I recommend that you include testing your tank as part of your maintenance routine.
How did you cycle your aquarium? Let me know in the comments below!
I’ve been keeping fish for over 30 years and currently have 4 different aquariums – it’s an addiction. I’m here to teach you everything there is to know about fishkeeping.
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.