1 watt per gallon.1inch of air stone per gallon.You could probably get away with half that as cold as you have it. 75watt low 150watt recommended up to 2 watts per gallon extremely aggressive 300watts.Man that is a huge reservoir.
you should a get a pretty strong air pump and at least 4 airstones and just to let you know water tends to hold a alot more water at 60f thats y usallly keep my temps at 60f i get a bigger harvest