I have a small pond and a 5000 gallon stock tank that I raise fish in for food and pleasure. I made a simple filter out of a plastic 55 gallon drum that seems to work much better than the many commercial filters that I have tried and is considerably cheaper to build. I began by cutting the top out of the drums with a sawzall. I then used the top as a template to cut three circles out of those light-diffuser ceiling panalswith the little squares (the left-overs make great shell holders for reloading) . I installed a 1.5" valve near the bottom of the drum for flushing and a 1" inlet fitting about a foot from the bottom. I then placed a milk crate in the bottom to create a space for floculation to collect and put one of my little cut-out panals atop of it to hold three bags of Lava-rock. I then placed a second panal with two bags of that Walmart variety pillow filling synthetic stuff, the third panal with a layer of charcoal brickets and a 1.5" discharge fitting near the top of the drum. The discharge gravity flows down to my waterfall and I have several aquatic plants in the top of each filter to help out a bit. I use a 110 volt submersible pump that I got at Lowes for around $60.00 but it is guarenteed for two years My formerly green pond is now filled with water as clear as gin and the fish seem much happier.