While on vacation in San Francisco, I got a chance to visit the Ocean Aquarium fish store. The owner there was very nice and told us told us lots of information on how to keep maintenance low in the hobby with deep gravel substrate. We picked up a few bags there and now have to replace the black sand in my 20 gallon with the gravel we bought. I don't know if we should take the fish out or replace it with the fish in. We have corydoras, green neon tetras, a honey gourami, 2 nerite snails, and a hillstream loach. If anyone has done this before, could you help me what to do?