Good homemade bio-filter media?

Sounds like a good setup.. I have a biofilter I bought of Ebay some time back... it actually just uses sand (pool filter sand) which has a large surface area... the pump pushes water in at the bottom, forcing it throught the sand, and them pushes it out at the top. I guess you could also use gravel if the pump was strong enough...just place your sponge at the end of the hose placed under the sand to help disapate and spread the water current out at the bottom.