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Biological Filtration

Mechanical filtration is meant to take particles out of the water, nothing more. Usually mechanical filtration is confused with biological filtration because the same media is sometimes incorrectly used for both types of filtration.

Biological filtration is that bacterial conversion of nitrogenous compounds described above in the nitrogen cycle. Where you want to clean your mechanical filter vigorously and often, the biological filter performs best when it can be left strictly to its own devices with a constant flow of particle-free, oxygenated water through the media. There are many types of biological filters. The canister filter, which has been the mainstay of the advanced hobbyist, the trickle filter, which made its bones in the salt- water hobby, the simple box filter, which is used with tremendous success by experienced fishkeepers reluctant to give up on a filter that has been keeping fishes alive and well for the past fifty-odd years, the newcomer on the block, the fluidized bed biofilter, and many more.

Some tanks are maintained for years with nothing more than a simple sponge filter and air pump. The sponge filter is gently squeezed in a bucket of tank water once a week and the resident nitrobacters do a fine job of converting the ammonia and nitrite. Regular siphoning of uneaten food and fish waste goes a long way to helping you keep a healthy tank with a very simple filtration set up.

As many different types of biological filter as there are, there are more types of media. Some examples of biological filter media include plastic hair curlers, "bio beads," gravel, sand, sintered glass, ceramic noodles, and so on. Biological filtration is critical to the health of your fish. Whichever media you employ to harbor your nitrifying bacteria, remember that you want to keep the bacteria safe from harm. It takes about six weeks for the nitrobacters to establish themselves in the filter.

During this critical period, the ammonia and nitrite will reach high, maybe toxic levels. Keep your fish load very low in the new aquarium and be very careful not to overfeed. It is suggested that the tank be run with one or two very small and inexpensive fish during this period. The water may cloud up for a period, new tank syndrome. This is normal and will clear up presently. Once your filter bacteria have become established, the water will clear up spontaneously.

To maintain a healthy bacterial colony in the biological part of your filtration system, treat the media with gentle care. When cleaning the media, use only tank water. Do not use hot water or fresh tap water.

A gentle rinse with tank water should be all you need to do if you have set up the system properly. The goal is to maintain the bacteria as undisturbed as possible on the media. If your tank is without power for any length of time, it is entirely possible that your biological filter will crash. This happens when the bacteria are without oxygen for a period of time. This time period varies depending upon a number of factors, but should you find that the filter has been off for a day, smells foul, and the fish are gasping for air at the surface, do not simply turn the filter back on!

The filter has become toxic and must be thoroughly cleaned and the media replaced before it can be used on the aquarium.

Written by Mary Ellen Sweeney