Sponge Filters

You can get a Azoo biofilter 2 sponge filter for as little as $9 and they are great for maintaining because you can remove the sponges without taking the whole thing apart.  http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=3936&N=2004+113424  Here is how you can make a do it yourself sponge filter  - I suggest using 1 inch thinwall PVC pipe  but you can use a smaller diameter 1. Make a base using a PVC flange fitting on the bottom The flange on the bottom needs to be sealed. You can use silicone or another PVC fitting. If you are lucky you can find a nice flat base flange fitting that is also already sealed. - something like this that will provide a nice base http://www.lascofittings.com/files/Catalog/images/851.gif 2. Cut a length of PVC pipe to push into the flange fitting and the pipe needs lots of little holes drilled around it where the sponge will sit. Drill another hole near the top of where the sponge will sit that is a tight fit for an airline hose entry 3. Now to make the sponge - soak the open cell sponge material and place in the freezer to make it solidify. Once it is frozen, take it out and drill a hole down the center that is slightly smaller than the outside diameter of the PVC pipe Assembly - 1. Seal the bottom flange fitting 2. Press the PVC pipe down into the flange. You may have to deburr the edges of the pipe to get it in. 3. stretch the sponge over the pipe to the desired location above the flange but covering all the small holes in the pipe 4. Push the airline through the larger hole at the top of the PVC pipe, above the sponge and force the airline down near the bottom of the sponge inside the pipe. 5. Install some gravel down the middle of the pipe to help weigh it down, but this gravel should be only as high as the bottom of the sponge where the airline outlets. You can also pile gravel / sand around the outside base of the flange to further weigh it down. 6. Plug it in and let it bubble You can install an air stone on it, but this makes it a little less effective as that slows water flow rate because an air stone is a restriction for air flow traveling up the PVC pipe which creates the suction to pull water through the sponge