Bullfrogs will quickly outgrow tanks. i raised one from a tadpole years ago, and the most humane thing we could do when she got near adult size was to donate her to a nature center, where they housed her in a pond.
Bullfrogs do not do well in captivity like other frogs; they will rub their noses raw on a screen lid, try to go through glass, and can get out of a stock tank easily.
Horned frogs; they do fine in a 10g tank for life. I keep mine in an equivelantly-sized tub/lid, because it retains humidity beautifully.