Just found this post and thought I would offer some advice. First he/she needs land. Bull frogs are not completely aquatic. I have a frog pond and have large numbers living around it. They only go to the water to breed. They live "around" water not "in" it. They still need moist areas, not wet. Plenty of plant life and shelter. A clay flower pot laid on its side, half buried, with lots of plant life around it works great. Logs with bark are good. They are very sensitive to chlorine and chemicals. Tap water will not work. Rainwater, spring water, or other pure water is needed. Bull frogs do not make good captive pets. They seldom survive long in aquariums. That is why they are not sold as pets.
It would be best to release him and get a pet frog from captivity.