Freshwater

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Part I: Aquarium Basics
Taking the Mystery out of Filters
Filters play an essential role in performing mechanical, biological, and chemical
functions in your aquarium. Some filters cover only one function; others
may do two or three.
The three main functions of a filtration system are to
Promote the nitrogen cycle (which removes unwanted ammonia and
nitrites from your system) by providing a medium for bacteria growth
Remove debris and waste from the water
Aerate the aquarium’s water by producing water flow and bubbles. By
adding these bubbles, oxygen goes into your tank, and eventually CO2 is
removed at the surface through gas exchange.
When you check out the astounding number of filters at a pet shop, you’ll
probably want to reach for the aspirin by the time you get to the second or
third shelf. But don’t worry, filters really aren’t as complicated as they may
first seem.
There are three types of aquarium filtration, and whatever system you decide
on needs to incorporate all three of them:
Mechanical
Biological
Chemical
You accomplish this balance by combining different filters, or by using one
that performs all three kinds of filtration.
Mechanical filtration
Mechanical filtration removes solid wastes and debris suspended in the
water by passing it over materials, such as synthetic foam or nylon fiber
floss, which captures small particles. Basically you are removing dirt and
other bad floating materials from the tank with mechanical filtration.
In time, this same filter can perform biological filtration when the surface
area of the filter medium (the foam or floss) becomes covered with beneficial
bacteria. The medium is usually contained in a small cartridge that slips
inside of a power filter unit, or is added in bulk form from a bag or box, as
with a corner filter.