When I use to use filter pads in my wet/dry, I would buy something they call batting here. It's similar to what you'd use to stuff a pillow with, but I got the stuff that came on a roll about 4ft tall, was 3/4 inch thick and you could buy it by the yard. Probably similar to the stuff Shane and John is referring to. We pay about $4.00 for a yard of it here so it is cheap as dirt and does the trick and goes a long way. Eventually though, I am one of those people who doesn't like to leave stuff like that in too long so eventually I removed every sponge I could find in my system out of the tank. I didn't want the hassle of changing/cleaning them every 3 days and went so far as to removing the pre-filter sponges off of my pumps even
Anyways, here's a picture of what I am talking about. You can get it pretty much in any fabric store.
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