A slope in the gravel? I just move gravel over with my hands in the tank without draining it, then either add more gravel because the front is to thin for your liking or just make everything even and clean looking.
Yes gravel lol the problem is... I want to add another 12 pound bag of gravel, and everything is already set up in my tank. That's what I meant how would I remove all that without draining all the water?