I've always thought the best place to put a filter is under the gravel. So in anticipation of a tankful of messy oscars I decided to put this theory to the test. This is 12 square feet of poly batting quilt stuffing, better known as "filter floss" at 20x the price. A $10 piece of fluorescent light grating and misc pvc parts... A pair of $11 126 gph powerheads privode a strong but reasonable flow. The top layer is covered in a scrap of fiberglass window screen. I topped it with a nice corse gravel that will allow the oscar's mess to sink down out of sight. It's landscaping quarts "pea gravel" and it costs $2.50 for a 50 pound bag.