A 72 gallon bowfront is about 23 inches high, and about 48 inches long. A 48 inch long Finnex Ray2 would give you about 60-70 micromols of PAR, if you have 3 inches of substrate, and the light sitting right on top of the tank. That is high medium light. A Fugeray would give you about 45 micromols of PAR, which is still medium light, but low medium, a very good level to shoot for. It would take only one of those to light up the whole tank pretty uniformly. If you use the legs that come with the light, the PAR would drop to around 40. You will need to use Excel with that much light to have a good chance of avoiding lots of algae.