So I purchased some course foam from the local fish store a year or so ago, and just got around to using it.

I have just changed an old Marineland hang on back filter with an Aquaclear 110. I took and cut a block of the foam about three inches long and cut a cross in the center of that block so I could slip it over the intake for this filter to use as a pre-filter.

One of the advantages of this is keeping uneaten food out of the filter. Surprisingly the Blue Rams and plecostomus have learned to come get a meal off of the food stuck to the foam. The Schwartzi cories will go huddle under that filter intake during feeding and also clean food off of the foam.

Foam is an inexpensive prefilter. Previously I have used women's nylon stockings as pre-filters by rubber banding the stocking to the filter intake.