Mine never come out of the water, although they have the opportunity. They also are growning well without a UV light. I have a common musk (Sternotherus odoratus) and a giant musk (Starotypus salvinii). I've seen common musks kept in traditional aquariums with fish, but I have to admit it was at a petstore (for several months, though). However, UV may have some benefits and can't hurt. Some types or individuals may bask more than my guys.