First Tank Guide Tank Logo
First Tank Guide Home

What Does My Filter Do?

Filtering Your Aquarium Water

(The First Tank Guide)

Why Do I Need a Filter?

The purpose of the filter on your aquarium is to remove excess food, decaying organic matter, free-floating particulate, dangerous chemicals, and the fish's waste products from the water.

The fish excrete waste constantly as they swim around in the water. If this waste is not removed, the toxins that the fish are removing from their systems will rapidly build up to high enough concentrations that the fish will poison themselves. Early stages of this are called ammonia stress - when it becomes fatal, it is ammonia poisoning.

In addition, particulate floating in the water and decaying food and other organic matter can contribute to cloudy aquarium water if not kept in check.

These pages are provided to answer some basic questions about filters, including 1) what different filters are, 2) how different filters work, 3) what normal maintenance is required, and 4) what are some advantages and disadvantages to the filter type.

Filtration Methods:

Filters clean your aquarium water in one or more of three ways: Biological, Mechanical, or Chemical.

Biological filtration is absolutely necessary in any aquarium to reduce the maintenance required. However, mechanical filtration and chemical filtration both have their places. Mechanical filtration helps maintain water clarity, and chemical filtration can take care of problems with your source water or can be used to remove specific toxins or any medication that is introduced to the system.
It is important that you are aware that your tank water can be crystal clear and still be toxic to your fish, or it can be murky or dirty looking and be perfectly safe!

It is vitally important to the health of your fish that you provide them with sufficient filtration. Filtration can make your tank look nicer and will greatly reduce the care required to keep healthy happy fish (a 10-15% water change once a week in a filtered system is much nicer than the 80-90% a day that an unfiltered system needs to stay viable). But filtration is no excuse to shirk on tank maintenance. Your fish will still need proper feeding, tank cleaning, water changes, and regular inspection for abuse, stress, disease, or any other problems.

There are many varieties of filters, including both submersible and non submersible models. You should select a filter that will fit your filtration needs and be appropriate for the type of fish you are keeping. Having multiple filters on a tank will usually give the best results and will provide backup in case of an equipment failure.

More information is available on these types: Hanging or power filters, corner or box filters, under gravel filters, sponge or breeder filters, canister filters, fluidized bed filters, trickle filters, and rotating drum filters. I also have information on protein skimmers (saltwater only) and Ultraviolet Sterilizers.

"My 3 year old daughter desperately wanted a fish so the family troops off to the pet store and buys - you guessed it - painted glass fish. I thought, "Wow, pretty fish." [It] never occurred to me the terrible things that are done to make them look like that. Now after [an] awful heart-wrenching morning explaining to my daughter her fish is in heaven with God, after only a week, I decided to look up these fish and see what I did wrong. Well I figured it out, my mistake was not researching what fish I was buying. A hard lesson learned at the expense of my daughter. I will never understand how people can justify hurting another creature solely for profit. Thanks for all the info on these lovely but mistreated little fish."
March 22, 2003
More Comments
"You have reminded me that it takes time and patience and if it ain't broke don't try fix it. Thank you for that. Your articles are well written, and for me just reconfirmed what I already know to be the best way to keep fish. I wish you good luck in anything you may do in the future."
November 20, 2013
More Comments