February 15, 2002, Newsletter Issue #2: All About Filters

Tip of the Week

There are three types of filtration: biological, mechanical and chemical. Biological filtration decomposes the toxic ammonia that fish produce as waste products. All fish tanks MUST have biological filtration; it is the cheapest, most efficient and most stable way to breakdown toxic ammonia.
Mechanical filtration traps such particles as plant leaves, uneaten food, etc., allowing them to be removed from the tank before they decompose into ammonia.
Chemical filtration (e.g., activated carbon, zeolite, etc.) can remove (under limited circumstances) such substances as ammonia, heavy metals, dissolved organics, etc. through chemistry. Chemical filtration is mostly useful for dealing with short-term problems, such as removing medications after they´ve served their purpose, or purifying tap water before it goes into a tank. A healthy tank DOES NOT require the use of chemical filters such as activated carbon.
The most important thing to remember is that all fish tanks MUST have bilogical filtration. Although chemical filtration can remove ammonia under limited circumstances, it are NOT a general solution.

Typical filters perform some or all of the three filtration types in series. Mechanical filtration (if present) usually comes first (where it is called a ``pre-filter´´), trapping particles that might clog remaining stages. Biological usually comes next, followed by the chemical filtration section (if present). Whether or not chemical filtration is useful (or even helpful) depends on who you talk to. It can be useful for removing fish medicines after their effectiveness has ended (partial water changes do the same thing though). They can also remove trace elements necessary for plant growth (with obvious results). Unless you have a good reason to believe that your circumstances require chemical filtration, avoid it.

Filters are not maintenance-free. For example, if debris is allowed to accumulate in a mechanical filter, it decomposes into ammonia, negating its primary purpose. Likewise, a biological filter´s effectiveness diminishes as it becomes clogged. Biological filtration requires water movement across a large surface area on which bacteria have attached (e.g., floss or gravel). The less surface area available, the less effective the filter. UGFs are cleaned by regularly vacuuming the gravel.
Canister and power filters are cleaned by removing the media and gently squeezing it in a bucket of used tank water (tap water may be used assuming it does not contain bacteria-killing chlorine.

There is no magic formula for what size filter one needs. Consult with specific manufacturer´s ratings and be conservative. You can´t have too much filtering (though you can have too much water movement), so err on the side of overfiltering.

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