Sponge filters are ideal for sand substrate. Sand is rough on hang-on-backs and impeller driven power heads. Not so much on canister filters because the impeller is on the clean water return side. Goldfish will sift through the sand and keep it pretty free of any uneaten food bits. They'll spit it everywhere, so you'll likely squeeze some sand out everytime you squeeze out your sponge filters.Thanks for the input! I also plan on doing a sand bottom, do you think this adds any effect to the filter setup?