+1, I just get the prefilter sponge for the Aqua Clear HOBs. Usually the one for 70 I can cut in half and make 2 pre filter for whatever I need. Plus it is only like $4 for both of themPfunMo said:I've never thought of buying a special pre-filter. I just cut a piece of foam or media to stick over the end. Much cheaper and throw away when I'm done with it.