Today I'm at my grandfathers house. He just had surgery so I'm going to do a water change on his 55 gallon tank for him, but I was shocked when he said that he has never vacuumed his gravel in the year he has owned his tank. The tank looks great he does monthly water changes and has only had one death since owning the tank. All the fishes look healthy. I also tested to water and everything is fine. I was going to go to the local petsmart and buy a vacuum and clean the gravel but I'm concerned there might be poisonous bubbles that might kill all or some of the fish. What do you guys think I should do?