Biological Aquarium Filtration

Biological aquarium filtration is the most important of all. The lack of effective biological filtration is probably responsible for the deaths of more fish than any other cause. The particular dissolved compounds controlled by biological filtration are very toxic to fish even at low concentrations.

In newly set up tanks, the effects of these compounds can kill fish very quickly. In aquariums that have been running longer but are overstocked with fish, there can be constant low levels of these compounds in the water. This creates chronic, long-term physical stress, resulting in diseased and dying fish.

To understand biological filtration, it is necessary to understand a basic process in the aquarium: the nitrogen cycle. Ammonia is one of the key elements in the nitrogen cycle. Fish produce ammonia directly both as a by-product of respiration and as a waste product from the digestion of foods.

Solid wastes are also converted into ammonia, which is why it is important to remove them with mechanical filtration. Uneaten food, plant materials, and other organic items that decay in the tank are also converted to ammonia. Ammonia, a nitrogen-based compound, is extremely toxic. In an aquarium, it can build up quickly and threaten all the fish in the tank.

Aquarium Filter Designs: Undergravel Filters

Biological aquarium filters, including under-gravel filters, function in a completely different way, and they have a completely different design. The Nitrosomonas and Nitrobacter bacteria necessary for biological filtration will colonize virtually every surface in a tank. However, there is usually not enough surface area in a tank to support populations of these nitrifying bacteria large enough to process all the ammonia that is produced in a typical aquarium.

 

A biological filter deals with this problem by making the natural nitrogen cycle operate more productively.

A biological filter has two main functions. It increases the amount of surface area available to the nitrifying bacteria, and it creates a constant flow of aquarium water over the colonized area.

The most popular kind of biological filter is the undergravel filter. It is relatively inexpensive, reliable, and very effective. An undergravel filter is really just a plastic plate that covers the bottom of the aquarium. The plate has many small holes or slots in it. The exact physical appearance varies from one brand to another, but all work on exactly the same principle.

The undergravel filter plate is covered with aquarium gravel. Located at each back corner of the plate is a lift tube that extends from the plate to the top of the tank.

Hard and Soft Aquarium Water

You should know if your tap water is hard or soft so you can adjust it if necessary for your aquarium. Hard water has a high content of certain minerals -- magnesium, calcium and iron salts -- and soft water does not.

The biggest concern with tap water, though, is what the city water department puts in it. Most municipal water companies add chlorine or chloramine to the water to kill certain bacteria that are harmful to people. Unfortunately, these chemicals are themselves harmful to fish and must be removed from the water.

Every pet store has a selection of chemicals that will easily dechlorinate the water. For dealing with chloramine, however, you need something a little different. Chloramine is a combination of chlorine and ammonia. When a normal dechlorinator is used at double the recommended amount, it will break the bond between these two compounds, neutralizing the chlorine but releasing the ammonia. The added ammonia may be more than the nitrifying bacteria in your tank's biological filter can handle.

The only way to handle this problem is to use a one-step water conditioner designed to handle chloramine. This product will break the bond between chlorine and ammonia and neutralize both.