How do under gravel filters work?

Answer

There are several things going on at the same time. First, you have an air-stone in a tube filled with water. The water is in the tube because air pressure pushing down on the top of the tank forces the water up the tube. When you force bubbles up the tube with the air-stone, it draws water up with it.

The tube is now acting as a siphon, drawing water out of the tank to replace the water that is flowing out of the top of the tube. In order to get IN the tube, the tank water must flow through the gravel because the intake to the tube is on the bottom of the filter. This downward flow of water draws with it all the debris that the fish leave behind. This action causes the gravel to grind up anything coming through it.

All this debris is left on the floor of the tank beneath the filter.

An added benefit of the under-gravel filter is that having all this organic debris under the filter keeps the tank clear of not only the debris, but also the micro-organisms that feed on it. You have a clearer, healthier tank.

But you should also keep a back filter running and use a diatomaceous earth filter occasionally.

- wjs1632 -

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