I used to have a IOUS tank too. Until the internal wall gave way. What I had was first layer cheap wool that I would throw after it clogged up, next layer was sponge, black color type which I bought from fish shop and cut to size, then last was the ceramic rings. I would wash the sponge every half yearly.
I believe if you want to recycle, then any sponge will do, so long as it traps dirt.
If you look at some of the monster tank setups overseas especially US where aquarium supplies are hard to find and expensive, they use 'pot scubbers' which are actually the dish washing sponge we use.
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