My parents have 2 large tanks where they keep their pond goldfish for the winter. There are about 40 goldfish and the tanks are a 75 gallon and a 125 gallon. There are 3 filters per tank and the water is always crystal clear. Theres gravel but I feel bad that's there's no decorations or anything. Do goldfish need decorations? If so, are there any decorations that are easy to clean and are soft enough not to hurt their tails?