Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I have used quite a few Aquaclear sponges, and some other sponges, pond supply, coarser cells.
Finer cells: There is a square foam sold for insulating around air conditioners. It is open cell. Sure it could collapse, but I do not use that one over the intakes. I have it in a canister.
Think of it this way:
You want to start with a fairly coarse cell size to trap the larger debris, then go to a smaller cell size to trap the smaller debris, then got to floss or something to trap the finest debris.
If you start with too-fine a cell size it will get clogged up way too fast.