So I bought a 125 gallon and was excited to get it up and running, and even though I didn't like the gravel that came with it I put it in anyway. However, the more I look at the gravel and the plans I have for the tank, the gravel just doesn't fit in. Is it possible to remove the gravel that is in the tank now and replace it with sand or different gravel without draining the water out of it and removing the fish that are in it? If it is possible, what would the easiest way to do it be?