An undergravel aquarium filter is a thin plastic grill with holes that sits on the bottom of the aquarium. Gravel is laid on top of the filter, but the space under the filter is open, allowing fish waste to drop to the bottom. Because the plastic filter has holes, sand is not traditionally used, as it falls through the holes. However, for aquarium owners who prefer the look of sand instead of gravel, a few adjustments will keep the sand on top of the filter.
Place an empty aquarium on a flat surface and put an undergravel filter tray on the bottom.
Insert an air lift tube, which is a clear and rigid plastic cylinder, into the hole in one corner of the undergravel filter. Push the tube into the hole until it stops.
Connect a clear flexible air tube to the circular projection at the base of the air lift tube. Plug the other end of the air tube into the air compressor and plug the compressor into an electrical socket.
Pour a 2-inch to 3-inch layer of gravel on top of the undergravel filter and smooth it out evenly.
Measure the length and width of the aquarium.
Unroll the gravel tidy mesh and cut it out to the dimensions of the aquarium.
Lay the gravel tidy mesh on top of the gravel, making sure that all edges touch the walls of the aquarium.
Pour a 2-inch to 3-inch layer of sand on top of the gravel tidy mesh and spread it out into an even layer.
Complete setting up the aquarium by adding any desired plants, decorations, water and fish.
Rinse all sand, gravel and aquarium decorations well to remove dust before placing them into the tank.