making your own filter is probably the easiest thing n fishkeeping! All you need is a block of open celled foam (upholstery shops are a good cheap source) a 1/2 to 1 inch tube and an airline. Cut the foam to a 4x4 inch block and cut a slit into the center. Take a small drill and drill lots of holes all the way around the tube and up the tube about 3 inches. Insert the tube into the foam block. Drop an airstone connected to an airpump into the tube and place in tank (you might need to squeeze the foam underwater several times to get it to sink). One simple and effective sponge filter!