Makes me wonder why the lady at the local fish store suggested 40 lbs of gravel for a 20 gallon tank. I thought it's like 20 lbs for 20 gallon, and 40 lbs for 40 gallon. UGF should be OK, and a hang on the back filter definitely would not hurt. With that much gravel, I like to push all that gravel towards the back, and make it look like a slide coming towards the front. That way you still see the fish when you view it from the front. Put those small flounders in there, some cory cats to clean up that gravel.