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You can use the sponge only if there is no chemical on it.
Make sure research carefully on how the particular sponge product was made before using it for aquarium.
What filter are you using? They usually sell filter media for each filter model at a decent price.
I had thought of DIY sponge as filter media too, but I couldn't risk it. Sometimes there is no way to find out what kind of chemical treatment the random sponge you buy had gone through.
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