I was given a tank that the prevouis owner must have used a green pad or something to clean the inside since there are scratches on all 4 sides of the inside. I read that you can use diffrerent grits of sandpaper to remove the scratches. Has anyone tried this? I didn't notice until I set the tank up and it has three fish in it. Should I take the water down below the scrathes..rub them out, vac the tank and return the fish to the tank. Will this work and be safe for the fish? Thanks for your input!