Chemical filtration is somewhat different when compared to mechanical filtration. Unlike mechanical filtration, we cannot see some pollutants in our fish tanks. A chemical filter involves more of a molecular filtration process where a certain media absorbs the pollutants rather than just catching or trapping it.
There are certain times in the hobby where you may need to run chemical filters on your tropical fish tank. Most hobbyists do not have chemical filters running all of the time. There are many types of chemical filter media available and each performs a special function.
Activated carbon or charcoal is the most popular chemical media used. The carbon acts as a magnet and attracts pollutants and then absorbs them. Activated carbon is usually used to remove medications that may have been used or tannins that leach out of your driftwood.
A chemical filter can be a special filter that you may have to purchase, or it can be a power filter that you already own. Many power filters allow for chemical media to be placed directly within them. Special chemical filters such as Phosphate reactors, multimedia reactors, or UV fluidized bed reactors can be purchased to help battle specific problems that may occur in your tropical fish tank. Each filter would be filled with a specific media type that you wish to use to help remove impurities in your water.
I would like to say that each of the above mentioned chemical filters do a great job, but you should never depend on chemical filters alone. Regular, large water changes will help remove any impurities in your aquarium tank. This is a mistake that alot of new fish keepers make. People tend to fall behind on water changes because they believe they have a chemical in their filter that will remove any impurities. The truth is that chemical media only last a few weeks to a few months. Therefore, the pollutants tend to grow in the water when you think they are being removed.
If you use a good chemical filter along with regular water changes, you should have very happy fish.
Please read Chemical Filter Media to ensure you select the most appropriate media type for your tropical fish tank.