Common musk turtles do quite well in deep water. They have been observed at 9m (29.7 feet), according to Turtles of the United States & Canada. So, any aquarium depth is not an issue, as long as there is sufficient place to rest at the surface of the water (they don't seem to float as well as the basking turtles). They are not as graceful swimmers as sliders, cooters, maps, etc. I have a hatchling musk and he loves to chase the bluegill around the aquarium. He hasn't caught any yet, but he seems to enjoy the 20" of water, chasing them to the depths and back up again. I do have plants floating at the surface and several places for him to hold on to. Part of the aquarium has a shallow depth (3") due to fixed driftwood. He will occasionally be found there, but the vast majority of the time he is walking on the bottom of the aquarium, hunting for food, surfacing for a quick breath and back down to the bottom.