Originally Posted by twocents
If you think polyester quilt batting would work, that might be another idea..
I'm no fish/aquarium expert, I'm a novice, so don't rely on my opinions about this. I've done patchwork quilting and the stuff I got from the aquarium supplier looks like quilt batting to me. Maybe a bit of googling would establish whether it is, in fact, the same stuff. My guess is that it is, but I wouldn't want to steer you down the wrong path. What bearwithfish says supports the idea, though.