If I was to purchase a 60" ATI Powermodule for a 72Hx 20Dx 18H mixed reef, how many bulb unit would I need? According to ATI I only need a 4 bulb but doesn't sound like enough?
The PM is extremely efficient, 4 would likely be enough for that tank. I would get the 6 bulb model so you can have a wider assortment of bulbs for color options.