If you get a sponge that has nothing added to it (nothing, it should say whether or not there is something in it.) Just a plain sponge that's soft, then it should be fine. I am using one in my bettas tank and he is just fine. I found it at walmart, it's blue and was to be used for mopping because it had a white clip on it. I just cut out the right size compared to the filter and rinsed it off alot before using it (to make sure it's clean.) Don't buy one that has no cover on it (something it's wrapped in, bare ones could carry bacteria.)
If you want do something else, like Lionmom said, you could try pingpong balls. It might work if your filter is set right, the pingpong balls will stay in place and keep the current slower. Or if they dont, maybe try putting suction cups on each one and stick it to the filter.
Yes, don't use a sponge if it says not for aquarium use. Nevermind me saying the second paragraph.....
Last edited by BlueHaven; 08-31-2010 at 04:56 PM.