Last update: November 12, 2022

How to use activated carbon in your aquarium!

What if I told you there was a magical ingredient that you could add to your aquarium filter?

… A magical ingredient capable of removing chlorine, water discoloration and even bad smells from your aquarium.

Well, that magical ingredient exists…

Activated carbon!

And today, I am going to teach you everything you need to know about it.

What is activated carbon, and what does it do?

A pile of activated carbon ready to be used in an aquarium

Activated carbon is essentially charcoal. That’s why you might hear it referred to as activated charcoal.

But what makes it so special is the way it has been treated…

Each piece of charcoal has been specifically manufactured so that it contains hundreds of tiny pores.[1]

To put it very simply, these pores trap pollutants, making activated carbon excel as a chemical filter media.

Which pollutants exactly?

In aquariums, activated carbon is commonly used to remove…

  • Chlorine and chloramines
  • Tannins that discolor the water
  • Phenols that cause bad smells
  • Certain medications

You should already be using a good water conditioner for freshwater tanks or reverse osmosis (RO) water for saltwater tanks to remove chlorine or chloramines during water changes.

But where activated carbon really shines is clearing up your water and removing bad smells from your aquarium.

Activated carbon is so popular that most modern filters actually ship with a carbon filter already installed. Those that don’t have made room for you to add it yourself, if you choose.

You should know that once the pores in the activated carbon fill up, it can no longer trap any more of these pollutants from your aquarium.

Because of this, you need to replace the activated carbon in your filter. I often do it during my regular maintenance routine. Fortunately, activated carbon is cheap and replacing it can be done in seconds.

How long does activated carbon last?

Well, that answer entirely depends on how dirty your water is. The dirtier the water, the sooner you need to replace it. For a well-maintained aquarium, many fish keepers replace the activated carbon in their filter once each month.[2]

To ensure the activated carbon in your filter lasts as long as possible, it should be placed after your mechanical filter. If you install the activated carbon before the mechanical filter, it will soon become clogged by the larger debris.

Oh, and don’t worry – activated carbon won’t leach any of the pollutants back into your water once it is full. While it is technically possible for activated carbon to release the pollutants, this would require some changes to the water chemistry that simple will not occur in your aquarium.[3]

So, don’t worry if you forget to remove the carbon from your filter – it won’t harm your aquarium. Activated carbon is perfectly safe.

What can’t activated carbon do?

Activated carbon is often praised as this miracle product that will save your tank from any problems that may occur.

I hate to break it to you, but it isn’t true.

Activated carbon cannot remove the following:

… You know, all the stuff involved in the nitrogen cycle. Water changes and other methods must be used to remove these toxins.

Activated carbon also won’t remove heavy metals, such as iron. If your water source contains these, use a water conditioner before adding the water to your aquarium.

And of course, you cannot “recharge” or “reactivate” activated carbon. I have heard so many stories about how you can put activated charcoal in your oven to restore it to as good as new… Don’t waste your time!

You cannot rinse them either. Once the pores on your activated carbon are full of trapped pollutants, it’s only suitable for the trash.

I would also like to add that if you don’t keep your tank clean and perform regular maintenance, all the carbon in the world is not going to save your tank!

What are the different types of activated carbon, and which is right for you?

Be mindful that activated carbon comes in a wide variety of shapes, depending on how it is manufactured. And, each has a specific use.

The most common shapes of activated carbon include:

The different types of activated carbon found in shops

From left to right:

  • Bead Activated Carbon (BAC)
  • Extruded Activated Carbon (EAC)
  • Granular Activated Carbon (GAC)
  • Powdered Activated Carbon (PAC)

In aquariums, you want to use Granular Activated Carbon.

Activated carbon can also be made from a variety of different ingredients, including:

  • Bituminous coal
  • Peat
  • Wood
  • Coconuts

In aquariums, you want to use an activated carbon made from Bituminous coal.

So, to clarify, when shopping for activated carbon for your aquarium filter, you want Granular Activated Carbon made from Bituminous coal.

Activated carbon made from Bituminous gravel for aquarium filters

Yeah, that’s the good stuff…

Why do you want this type of activated carbon over the others?

Well, this activated carbon has a superior pore structure for removing pollutants from water and is specifically designed for water treatment. In fact, if you have a water filter for your drinking water, chances are it contains Granular Activated Carbon made from Bituminous coal. Don’t settle for anything less!

And I mean it. I constantly see carbon pellets and carbon beads sold at pet stores as aquarium filter media made from all different materials. Don’t be suckered in by their cheaper price – they are the wrong tool for the job. Other types of carbon not only remove less pollutants but can also clog quicker.

One more thing before I move on – be mindful that some types of activated carbon contain phosphates. If your carbon filter contains phosphate, then it can actually leach into your aquarium.

And you don’t want that… Especially if you have a freshwater tank.

Many types of algae love phosphates, and elevated phosphate levels often lead to algae taking over your entire tank.

If your test kit reveals that your tank is high in phosphates and you can’t find any other reason for the elevated phosphate levels, try removing your carbon filter – it could be the culprit.

Lucky for you, my number one recommendation for best activated carbon contains no phosphates at all…

Which is the best activated carbon for your filter?

If you bought a brand name filter, chances are that the manufacturer also provided a carbon filter to fit.

The problem is that these filters often use inferior activated carbon and are expensive.

However, I have a better solution. And, it’s going to save you money!

Grab some loose activated carbon. My personal go to brand is Marineland…

Marineland activated carbon for aquarium filters

Okay, that’s step one done. But you can’t add it to your filter like this – the fine grains of carbon will blow around your aquarium.

Next, you need to grab a reusable media bag. These things are awesome! Fine mesh is best. Like these ones – make sure you choose the right size for your filter!

Fill your media bag with activated carbon and place it in your media. The bag not only holds the carbon in place but also makes it easy to remove!

Don’t forget to rinse any carbon filter before adding it to your aquarium. The small pieces rub together during transport, creating dust. You don’t want black dust floating around your aquarium, do you?

A quick rinse under tap water is all it takes to remove the majority of dust.

Bonus Product: Zeolite and Activated Carbon Blend

Remember how I told you that activated carbon can’t remove ammonia from your aquarium?

Well, if you blend it with zeolite, it can!

Activated carbon and zeolite filter media blend

Zeolite absorbs ammonia like a champ, and when combined with activated carbon, you get the benefits of both media in a single package.

Activated carbon and medication

So, you have a sick fish. No problem, add some medication to your tank, and your little pet will be better in no time – right?

That might not be the best idea…

You see, activated carbon actually absorbs many different medications, preventing them from benefiting your fish.

If you plan to medicate your fish, remove all traces of activated carbon from your tank.

Once the treatment is over, return the activated carbon to remove any leftover medication from the water.

Do you use activated carbon in your filter? Let me know in the comments below!

Ian Sterling

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.

Comments (70)

It works! My driftwood kept turning my tank brown. Looked yucky. With magic carbon in my filter, my water is always crystal clear.

Hi Azqua,

Thanks for your comment! Activated carbon does work great at clearing up tannins (the cause of your brown water) Did you know you can also boil driftwood before adding it to your tank. It reduces the amount of tannins it gives of!

Hello Ian,
I have bought few drift wood pieces from fish store which have been stored for last six months and they have white fungus. What should i do before placing them in my aquarium. I have read about boiling driftwood and bogwood. How about leaving them in low concentrated bleach water for some days and then let them sun dry. Any suggestion from your side is appreciated.

Hi Awais,

Boiling should work, but if that’s not an option, scrape as much of the fungus off as you can and soak it in a bleach solution. I’d then soak it in fresh water so that the bleach doesn’t leak into your tank. You’ll likely want to soak it anyway since your driftwood will float if it’s not waterlogged.

Hello there, good sir.
I’m kinda new to the hobby,and I’m really interested in driftwood.
Instead of boiling,can i just put the wood in a container with boiling water inside?
(Currently i don’t have a cooking tool big enough to boil a driftwood)
Many thanks for your answer.

Hi Jose,

Any soaking will eventually release the tannins, boiling speeds up the process. You can soak in cold water but it takes a looooot longer

Hello there. We have yellow water issue in our apartment and we are unable to resolve the issue. It seems due to high iron content the water is yellow
Does the granular activated carbon can be used as a solution
We use this water for our daily activities like washing and toilet use. But not for drinking

Kindly respond

Hi Veera,

Your iron levels sound extreme for them to be coloring the water. Activated carbon will not help here, you will need to use a water softener. I’d be hesitant to use this water at all as it may contain additional contaminants that will harm fish.


I am thinking of adding Activated Charcoal in my aquarium filter system, but the only space available for the Carbon is inside my UV light Chamber. Will the UV light damper or affect the performance of the Activated Carbon?

Thank you for your time!

Hi Krishen,

Any water that passes through the charcoal will be shadowed from UV light, meaning that it will not be treated. Otherwise, I understand that many air purifiers use the both of these together so it may be a possible solution if UV treatment is not important to you.

Hello there! Can you help me? First
1. I just used carbon media (EAC) and I put it in my external hanging filter and do changing all the water.But the water turned yellowish .I scared if the carbon will harm my fish.I don’t use and treatment medication just added some water conditioner and aquarium salt (to kill bacteria).Can you tell me what happens?
2. Can I use a thing seller recommend me to use (like a yellow wet powder) to clear the water back.I usually use andit works before .That time I don’t use carbon filter yet.

Hi Auni

1. Activated carbon shouldn’t turn your water yellow. If you can trace it to that, then it’s possible it hasn’t been processed properly or something else was mixed into it. Adding carbon shouldn’t change the color of your water.

2. Living in the US, I am unfamiliar with these products. It would depend on what the yellow is. If it’s dust or sediment, it will need to be filtered out. If it’s algae, you’ll need a different solution. If it’s something else, then you’ll need another solution again.

1. I think my TENSION GON (a product name, anti chlorine and quite expensive here) turn the colour to yellow.Maybe I can try another cheaper anti chlorine to replace it 🙁
2. Yah sorry I know what this seller recommend me.It’s alum to crystal clear the water back.Can I use while using carbon media?

Hi Auni,

Unfortunately, I can’t help you here. I have no experience with the products you are using. Is there a local fish club or fish forum you can ask?

Hi! I’m fairly new to the saltwater hobby. I’ve been trying to learn everything I can about the chemistry of it for water quality and everything else there is to learn about keeping a healthy reef tank. Unfortunately everything I read or watch is so confusing. I’ve just read a couple of your articles here and I love how you break it down so simply!! I learn better if I know the “whys” about things and you seem to do that in your articles. My question is have you done a fish tank 101 article for people like myself that know nothing about this? If not, have you thought about it?

Hi Debbie,

Thanks for the lovely feedback. I’m glad you have found these articles helpful.

Great minds think alike! I’m actually in the process of writing a giiiiiant article on how to set up a fish tank covering every single step of the process, including choosing tank size, products, cycling, chemistry, maintenance etc. Unfortunately, since this site is a hobby and life keeps getting in the way, it’s taking considerably longer than I anticipated.

I bought activated charcoal from online store. I have drained it repeatedly but it still gives out sligh black colored water. Is it safe to be used in cannister filter?

Hi A Pradhan,

It’s possibly safe to use, but if it is still giving off small dusty particles then you risk staining your water a darker color, until these tiny particles are filtered out.

Just discovered you and I was doing some self-educating. Thank you so much for your time and your knowledge I will be reading more from you

Hi Leena,

Thanks for the lovely feedback. If ever you have a question regarding an article here please pop it in the comments and I’ll help to the best of my ability 🙂

i just brought carbon the pellet type thats all they had in store. i put in net bag on top white filte songer . is that ok

Hi Cassandra,

If it was sold in a fish store then it was likely the right stuff. You are correct, water should flow through the sponge first before it reaches the carbon.

hi Ian! looks like I got another question for you.
I’ve used activated carbon to pull Melafix out of the tank. the carbon was only in there three days, then I pulled it out to add Paraguard.
my question is simply, can I hang onto this activated carbon and use it again when I’m ready to pull the paraguard out of the tank, or will I need to grab some new carbon to do the job?

Hi Shae,

If it’s used to pull out medication, I’m one to be cautious and dispose of it completely – fortunately, activated carbon is affordable if you are using the loose stuff.

more than fair! I thought about it after I went to bed last night too, and came to the same conclusion. I don’t want to reintroduce what’s ailing him, especially since I’m starting another treatment for what the Melafix didn’t fix. ><
thank you so much! I used my last pre-bagged cartridge of carbon getting out the Melafix; I'll get the loose stuff when I'm ready to pull out the Paraguard.

It’s less that you could reintroduce what’s ailing him and more the medication itself – we draw these out of the water for a reason!

Hello. I have an odor issue with my freshwater tank. I just broke it down completely, vigorously rinsed the substrate (tiny pebbles), rinsed/pruned/separates the plants, cleaned the filter box and used new filter (charcoal), cleaned the glass with vinegar (and then rinsed with water), dried it, placed the rocks, plants, filled, treated the water and an hour or so later returned the fish to the tank. I didn’t use hot water as I wanted to preserve the good bacteria. The tank looks great and the fish are happy and healthy, but the odor persists. Suggestions?

Hi Sue,

Have you tested your aquarium with an aquarium test kit? If so, what did the results return?

Also, when you say you have an odor issue, what does it smell like?

If fish are healthy and no medication is necessary, Is it okay to use activated carbon at all times in my HOB filter in a media bag between the filter floss and biofilter ceramic media? I saw some comment on a forum saying you shouldn’t unless necessary, because activated carbon removes beneficial bacteria. There is so much bad information on forums, so I appreciate your help. Thanks!

Hi Satchmo,

YOu would generally put activated carbon after the ceramic media. You can run a tank with activated carbon 24/7 if you want – there is no harm in it. It won’t remove beneficial bacteria.

I set my new Aquarium up on July 15 with gravel. I removed about 50% of the water and took the gravel out and replaced it with sand two days later because of the reviews on using sand. It was purchased from the pet store (white) and I cleaned it according to the instruction. Well, I filled the tank and treated the water. However, it got this crazy cloud/haze. I was told that the sand would settle and clear in a few days at the most. The tank did start to clear but not totally, just a little. I run a HOB up to 90-gallon filter. ( Aqueon) I have changed the filters twice; today being the second time because it was very dirty. I kept the old one in back of the new one to keep the spike of Bateria going. And I added the filer fiber. In addition, I added a sponge filter to filter on the opposite end of the tank. It’s been running for two days. Everything I read says it is a bacteria bloom and it can take days to months to clear. I used clarifier, and I test everyday. Numbers are good, but I still have that cloudy water. Should I add the carbon packs I purchased? Am I on the right path? Your feedback and will be much appreciated.

Hi Julius,

If you have used fine filterfloss to filter out the sand, and it’s still hazey color, then it very likely is a bacterial bloom. This is 100% normal during cycling. Once the cycling process is over, your bacterial bloom should be just about over too.

Unfortunately, a lot of fishkeeping comes down to waiting. Hang in there, it will be worth the patience!

I love the article! So if I put the carbon before the biomedia it’s not going to affect the beneficial bacteria that the biomedia lives off of? I have a tidal 35 filter and when I try to add the carbon last it just falls out of the filter lol! So I’m stuck with putting it in the middle but I can’t find a straight answer on weather it’s good or bad to have it in the middle! When I say middle I mean after the sponge and before the biomedia

Hi Scott,

It shouldn’t make a difference since carbon doesn’t absorb anything the beneficial bacteria should eat (ammonia or nitrite) The reason you see the recommendation to have it last is because it is chemical filtration. To keep things simple, when making recommendations to people, especially beginners, you’ll here Mechanical filtration -> Biofiltration -> Chemical filtration. The reason chemical filtration is put last is because there are so many different varieties, depending on what you want removed from the water, and some remove ammonia and nitrites. Ideally you want your biomedia removing these.

Thanks man! I’m using chemipure green, if you’ve ever heard of it. I’m sure you have though haha what are your thoughts on it if any? Im setting up a 10 gallon now no fish yet and plants coming in the mail tomorrow!

I have heard of chemipure green but I don’t have any experience with it. I am a little unfamiliar with what it *actually* removes or whether it is pure activated carbon. You would have to call for clarification – it says it removes “organic compounds” but doesn’t specify what these are. Depending on who you talk to, ammonia and nitrite could be called an organic compound, so this phrase without listing what it actually removes is a little ambiguous.

If it’s JUST activated carbon, then it’s fine to put before the biomedia. But once we get to chemical removing resins, it depends what that resin was designed to trap. Be careful here.

Also, I’m sure you are, but just want to make sure you are on top of cycling your tank before you add fish!

Hi Julie, depends on the cause. If it’s driftwood or organic matter, you’ll need something like activated carbon to remove it. If it’s dirt or sediment, you’ll need water changes etc. If you can find the cause, the solution will become apparent.

I filled premium activated carbon(marineland) in a hanging mesh bag and put it behind the Aqueon filter cartridge four hours ago and yet my 20 gallon acquarium is still cloudy. How long does it take for the water to clear? Should i hang the mesh bag in a different location.

Hi Fazel,

Is your tank new and cycling? If so, that is probably bacterial bloom and not caused by the activated carbon.

hello, i would like your opinion on Anthracite charcoal , i read is better than Bituminous. anthracite is used in labs..
thanks for the article and i love how you write.

Hi Agustin,

Excellent question. My understanding is that Anthracite is a coal (dig it up from the ground) and is very different to activated carbon (burnt wood) which has all the tiny pores needed to trap chemicals.

Hi Hamid,

I have seen plenty of discus tanks that use activated carbon to keep the water clear.

Hi Ian
I am a novice Tropical fish Keeper. I have just followed instructions on my Activated Carbon that I purchased for my 240ltr tank. I soaked carbon in water for an hour to release excessive dust. I then placed carbon in fine mesh bag. I out bag in the Dj al stage of my filtration system. Next morning I have tiny particles of charcoal laying on top of my white gravel!!! I am horrified at thought this could harm my fish when it has finished cycling and I add some fish. Is this the case or will the fish be ok? Should I empty tank and wash gravel? Your expertise in this matter would be greatly appreciated. Thanks

Hi Jan,

Don’t sweat about it, this shouldn’t be an issue. Best of all, you don’t need to empty your tank. A quick gravel vac should get rid of all the tiny particles resting at the bottom of the tank. If you find tiny bits floating through the tank, put some filter floss (50um) in the filter and this will get rid of the free-floating stuff.

Any idea what is in ciano filter cartridges?
I want to put some anti fungus treatment in my small tank, need to remove carbon but I don’t know what contains carbon.
I have ciano cf40 filter with aqua clear and bio bact filter media plus foam.
I’ve also seen some foams described as carbon I think? Does the foam contain carbon? (I suspect it doesn’t)
I’ve also sent a query to ciano, waiting for their reply

Hi Karen,

I am unfamiliar with Ciano filter cartridges. If it’s a disposable filter cartridge, like all others, I don’t recommend them.

Hi Jason, good question.

1/2 cup of activated carbon per 10 gallons would be a good starting point.

I just got back into this hobby too and boy am I learning alot this time around. I have 4 tanks going ,a 20gal tall,a 20gal long, a 10gal and and a 5gal. I crashed my 20gal tall c0ause I didn’t know anything about a uv light and killed all my fish all of your advice is so very helpful. I am so glad to find this site thanks 0for the info.

I have a 165 gallon Goldfish tank. I just used kanaplex and metroplex with focus to feed the medication because i had parasites and white stringy poo. I am almost through the treatment. Mt water has gotten just alittle cloudy. I run an FX6 canister on this tank but do not want to put carbon back into the canister. Can i just hang a bag temporarily in the tank in an area that has flow to remove the cloudiness and any left over meds? This would allow me to medicate in the future without having to open and get into my canister.

Hi Catherine,

You can, but depending on the flow it may remove contaminants slower or less effectively.

I’m glad I found your site. I’ve had many fish tanks over the years and have learned a lot through trial and error to be sure (especially in the earlier years). I recently set up a small 20 gallon freshwater tank and realized I’d forgotten a lot of what I’d learned on previous tanks.

I remember I always used Zeolite and Activated Carbon in my filter. I buy them in bulk but separately and make my own mixed filter bags (a lot cheaper as you mentioned). My fish are doing great, actually better than great! Just a couple of Lyretail Molly, 5 Rosy Red minnows that were bought as feeder fish for a turtle that I rescued (turtle released back to his pond) and are now fully grown, a gourami, a loach and a now ginormous Pleco that was the turtles friend!

My question is this. Can I run the Zeo and the Carbon all of the time?

PS Also I am a big fan of Vortex Filter with Diatomaceous Earth and run it almost every week for about 12 hours. Is that acceptable or is that an overkill?

I also made the mistake of buying food grade Diatomaceous Earth. It doesn’t work in the Vortex filter … way too fine. I had to order Diatomaceous Earth from Vortex but they are charging $19.99 for 5 lbs. I bought 20 lbs but I’m sure I could have gotten it cheaper somewhere else. Any suggestions?

Hi again, Tony.

I’m of the opinion that you can never have too much filtration. I personally use micron filter pads in favor of a Vortex Filter as it’s a cheaper solution for polishing water. Weekly at 12 hours likely isn’t overkill, since it’s sole job is to filter out the really tiny bits of gunk. You tend to stop running these once you notice a difference in the clarity of your water. On the buying side, it’s a little pricey but at least you are assured of it’s quality. You can grab it on amazon for almost half that, but as always I would be very cautious when it comes to anything that touches your aquarium water.

Hi Tony,

Welcome back to the hobby! It sounds like you have a very lively tank. Many fish keepers choose to run Zeo and carbon all of the time, replacing them reguarly. I choose not to since they can hide the appearance of problems. For instance, an ammonia spike can indicate that something is wrong with your tank, but if the zeolite is absorbing all the ammonia, then you may not even be aware the problem exists. This of course is a personal choice for ease of diagnosing. It’s also an added ongoing cost. However, that isn’t to say that using it is wrong – if you find that it makes maintaining a tank easier, then roll with it!

I just got back into this hobby too and boy am I learning alot this time around. I have 4 tanks going ,a 20gal tall,a 20gal long, a 10gal and and a 5gal. I crashed my 20gal tall c0ause I didn’t know anything about a uv light and killed all my fish

Hi Philip,

I’m so happy to hear that the advice given here also worked well for your pond! Thanks for the lovely feedback.

I bought the Marineland activated carbon and a roll of 100% polyester batting and made my own filters for my 5 gallon fresh water tank. I think this has made my old sword plant even bigger and healthier and not caked in algea as much. And the tank smells cleaner. Your article reassured me of the type of carbon that I bought was the best, thank you.

Hi Virginia,

Thanks for sharing your experience. Your tank sounds really healthy. Good work!

I use the carbon filled filter cartridges in my (2) hang on back Marineland Emperor 400. Change them out monthly. Can I cut the cartridges open, dump the charcoal and refill with ammonia neutralizing blend and reuse until the poly fiber is worn? The fiber looks like it can filter much longer than a month and I rinse and reuse Them before replacing, even then the fiber looks good. I’m thinking the charcoal is what requires the monthly change. What do you think? I have a 135g w/ (5) 4 inch Indo Datnoids

Hi Val,

Disposable cartridges are a scam. Every time you throw them out, you lose the good bacteria inside. A healthy aquarium shouldn’t need activated carbon. With proper maintenance, Aqaurium sponge can last up to a year and ceramic rings for up to 3 before needing to be replaced. This way, you are not locked into buying monthly cartridges. If you need a filter recommendation, check out the aqua clear filters.

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