I have used egg create for that before. I have a undergravel filter in the 220, so the big holey rock is sitting on it. Now if I could just convince my Tangs to stop digging rocks, everything would be great!imthedad;4812342; said:Loving the tank. As a side note, I use the white plastic diffuser grid from Home Depot for any rocks so that they dont touch the bottom of the tank. It stays covered by your substrate so you never see it. even with all the digging... Good and cheap insurance policy. Just my 2 cents