That's a lot better than using the undergravel filter backwards as I tried to do. What a pain in the a**!!! I don't think exposed areas of the UGF will be a problem. Add a little more substraight and/or fill the holes with your hand or something. I have 2 pairs of talapia which dig holes that are about 4 inches deep and big as a frisbe and part of the filter does get exposed, but I don't think it's a big deal. Concerning canister filters: I have a couple large Rena Filstar 3 filters which I bought for $120.00 each and they're rated for 170 gallons. This is the biggest avaliable from that maker and it's a lot cheaper than the Fluval 405, fluval's biggest I believe which has a max capacity of 100 gallons and runs about $200.00. The ones I got are very quiet and have stacking trays which are better than the Magnum which has a filter column and isn't as good a design IMO. Rena Filstar was the best deal for the size and price from what I had to choose from.