For me Ive found the greatest success with water over 85. Water will always adjust to the temperature outside over time. A small puddle like they would encounter in the wild (They could drown in a large puddle) will be moving in temperature almost exactly equal to the change in temperature outside. Over 90 degree days are very common in the tropics and I think it is probably a way frogs will naturally regulate their bowels in nature. By hopping into a nice warm puddle.