An undergravel filter provides biological filtration in fish aquariums. This system is popular, especially for small tanks, because it's simple to set up, economical and low maintenance. The undergravel filter consists of a raised plastic plate with perforations that sits on the bottom of the aquarium and is covered by gravel. Tubes are connected vertically, and air is forced through smaller tubing, by an air pump, while it exits through the larger tubes. As it does this, it pulls particles through the gravel under the filter.
Start with a clean empty aquarium. Clean all of the tubing and the filter in clear water. Don't use any soaps as they could be toxic to the fish.
Place the plastic plate in the bottom of the aquarium. Make sure that you have the proper size filter for the tank. It should completely cover the bottom with the solid side up.
Connect the small air tubing to the plastic plate on the provided nozzles. If the fit is too tight, heat the tubing at one end by holding a lit lighter a few inches away for about 5 seconds.
Connect the large tubes to the plate and run the air tubes through them. If there are caps on the top, place them on the tubes.
Attach the other end of the airline tubing to the air pump. Trim off any excess tubing.
Put several inches of gravel over the plastic plate. Add water. Wait 24 hours and add fish and plants.
Clean your filter periodically buy stirring the gravel and suctioning off the debris.
Avoid disassembling your undergravel filter for cleaning unless absolutely necessary. The filter builds up good bacteria and creates a healthy environment for your tank.