We've had our 55 gallon tank for about 7 months. It currently has a sand substrate, which I really hate and it's a pain to keep clean. It never looks "clean" to me. I really want to switch to a gravel bed, but I'm worried about how to do this in a way that won't desperately stress out the fish. We have 1 oscar and 1 pleco (both are nearly 4 years old). I feel it will be really hard to take all the sand out without draining the tank, but how bad will that be for the fish? I can move them to a small tank while we clean it but will fresh new water be detrimental to them? Our filter has a bio wheel so I was wondering if that would help at least keep their good bacteria in the new water, so it's not at total shock to their systems. Any advice, tips, or suggestions?