Chemical filtration is the creepy uncle of the aquarium world.
It may not be popular, but if your aquarium is facing an emergency, you will be glad you have it.
So, let’s take a closer look at chemical filtration and how it can be used to benefit your aquarium…
What is chemical filtration and why do you need it in your aquarium?
As the name suggests, this is a filter that specifically removes chemicals from your aquarium.
Now, you may be thinking:
I don’t need that because I don’t have any chemicals in my aquarium!
Well as it turns out, you do…
When most people think of chemicals, they think of man-made ones such as laundry detergent, bug repellent or antifreeze. I’ll agree, none of these should be in your aquarium. 
But it turns out nature is just as good at creating chemicals!
Guess what? All of those are chemicals!
And you can use a chemical filter to remove them from your aquarium.
But chemical filtration can do more than just remove chemicals.
Depending on the type, a chemical filter can also remove other pollutants – some of which are just an eyesore but others of which can quickly kill…
- Heavy metals, such as copper
- Compounds, like sodium chloride (salt)
- Medication used to treat sick fish
- Tannins from driftwood that discolor the water
Did you know? Many of the pollutants that can be filtered out by a chemical filter can also be removed bywater conditioners.
What is the best type of chemical filtration?
It is worth mentioning that there is no best chemical filtration. The right chemical filter for your situation entirely depends on the pollutant you want to remove from your aquarium.
With that out of the way, let’s take a closer look at four of the more common chemical filter media.
1. Activated carbon
Does that name ring a bell? You have likely heard it advertised in beauty products claiming to make you look 10 years younger. I can’t comment on its effectiveness in that situation, but it can certainly help pretty up the water in your aquarium.
Also known as activated charcoal, this is the most widely used chemical filter media. A big reason for activated carbon’s popularity is that it can deal with a wide variety of pollutants and is readily available and affordable.
So, how does it work?
Well, each piece of activated carbon has been processed to create hundreds of little pores, which are actually holes. These pores are so small that you cannot see them with the naked eye.
These tiny pores trap pollutants, removing them from the water column.
Activated carbon removes:
- Chlorine and chloramine
- Dissolved proteins
- Water discoloration
- Bad smells
Zeolite is a natural volcanic rock that is mostly made up of silica and aluminum.
For chemical filtration, however, you are more likely to come across artificial (man-made) zeolite. This isn’t an issue, since it performs near identically to its natural counterpart.
Zeolite also has hundreds of tiny pores, but it works is a little differently compared to activated carbon…
It doesn’t just filter out pollutants, but it instead makes an exchange. When zeolite takes in ammonia, it swaps it for sodium. This process is called ion exchange.
The exchange continues until the zeolite has no more sodium to swap.
Zeolite is most commonly used in freshwater aquariums, with many hobbyists loudly advocating that it will not work in saltwater. However, a study by the EPA suggests that zeolite still works at reducing ammonia levels in marine environments, just not as effectively as in freshwater.
Some brands combine both zeolite and activated carbon to form an all-in-one chemical filter blend that can remove almost any pollutant from your aquarium.
Believe it or not, rusted metal can actually be used as a chemical filter media.
Both aluminum oxide and iron oxide can lower phosphate levels in your aquarium, which can clear up algae problems.
However, evidence suggests that aluminum oxide, like Seachem Phosguard, leads to increased aluminum levels in a saltwater aquarium. Saltwater tank owners should use ferrous oxide instead. 
Resins are widely used in water softening and water purification, so it’s no surprise to see them make their way to the aquarium hobby.
Like zeolite, resin filters work by using ion exchange. However, they are capable of removing many more pollutants.
Man-made resins are manufactured to remove specific chemical wastes including phosphate, nitrates and heavy metals.
Because resin has hundreds of tiny little pieces, it will require a media bag – otherwise, it’s just going to float around your aquarium without effectively filtering your water.
Depends on the resin filter
A warning before installing your first chemical filter
A chemical filter is not an unlimited resource.
There will come a time when your chemical filter will become full – no matter what type you use.
And when this happens, it will no longer absorb pollutants from your water. In fact, the opposite can happen…
Your chemical filter can start releasing pollutants back into your aquarium.
So, whether you like it or not, you will need to continuously swap out your chemical filter. Some last weeks, others months, but the time will come when your chemical filter can no longer perform its duty.
For this reason, I recommend trying your hardest to fix the cause of the pollutants – it will be well worth the effort…
After all, when there are no pollutants in your aquarium, you won’t need a chemical filter, right?
If you do find that you must use a chemical filter, read the manual for how often you should swap it out. By following the instructions, you won’t have to deal with the disaster caused when a chemical filter stops working.
Do you use a chemical filter in your aquarium? Have something to add to this discussion? Let me know in the comments below!
Ian Sterling, founder of Fishlab.com, began his aquarium journey over 30 years ago, driven by a deep fascination for fish and their diverse personalities. His website, Fishlab.com, is dedicated to making fishkeeping accessible and enjoyable, offering beginner-friendly guidance, expert insights, and a community for aquarists to connect and share experiences.