I am not sure why Tortoises all flip on their backs, but they do. Usually they are either climbing over each other, a large rock, on they are trying to escape their enclosure. Make sure they cannot see out of their enclosure,aquariums are not a good place to house them. Also make sure they have a place to hide. Small huts, or another enclosures for them to get out of the sun, rain, or other critters. Give them a place to feel safe, is the best way to calm them down so that they are not trying to climb out. Good Luck!