07-27-2011, 11:56 AM
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Some more specialized LFS will carry foam blocks. You can cut them to the sizes you need. It saves some money. However, one of the most important parts of using a sponge is the mechanical filtration aspect of it which affects the flow of the water. If you are just looking for biological filtration, you can buy ceramic rings, as someone suggested, and put it in a nylon mesh bag. The ceramic media is extremely porous and offer huge amounts of surface area for bacteria and will do an excellent job of giving you added biological filtration without slowing down your flow rates.