This is a very simple yet effective DIY filter that can handle the waste of a goldfish tank. The filter media can be altered to meet you needs and budget. The first one I build years ago had lava rock and quilting batting as the filters. Bio balls are much cleaner and the next one will utilize matala mat in addition to the polyester pads.
The bio chamber is one cubic foot. The glass pane is about ¾ inch off the bottom. The smaller pane is siliconed to the sides and bottom but the bottom corners are mitered so the allow water to drain.
The bioballs rest on egg create.
Polyester pads complete the filter.
Another view.
Final install.
The guy I built if for confessed to me after buying a dozen more fish for his tank “David, I'm sorry I doubted you. I’ve got to tell you I thought you were selling me a lemon, but this thing rocks.” The tank is a 220 gallon and has 25 large sarassas and wakins. It is equipped with automatic daily water changes an is plumbed to a floor sink under the tank.
