LEARN ABOUT AQUARIUM UNDERGRAVEL FILTERS

Undergravel filters are usually the first and primary filter used by the beginner aquarium hobbyist.

They are a simple solution to the complicated filtering needed by any reasonable-sized aquarium.

The filter "plate" is placed under the gravel. Tubes from the plate contain an air stone attached to the air pump (outside the tank). The air pumped through the air stone at the bottom of the tube creates an upward current of of water that draws water from underneath the filter plate up the tube and back into the tank.

As the water is drawn from the tank, down through the gravel to the underneath area of the plate, it is filtered. Large paraticulates such as uneaten food and fish feces are left on top of the gravel (they are too large to get through the tiny gravel pores).

Additionally, bacteria live in the gravel - bacteria that thrive on the biological waste from the fish metabolism and waste. The bacteria "eat" the ammonia and nitrite, turning it to a less toxic type of ammonia and nitrate (a good plant fertilizer).

The main drawback to undergravel filters is that they are not adequate as the only filter for a large tank (more than 15-20 gallons of sparcely populated tank). They also require more laborious maintenance than most other types of filters. Because the large particulates are trapped on TOP of the gravel, frequent gravel vacuuming is necessary.

Because they do not hold enough surface area for a large amount of beneficial bacteria, they do not cleanse the tank of enough toxic ammonia and nitrite for fish health. More fish die from ammonia build-up than from any other water problem.