Coral only requires so many hours of light to complete a photo period. During this time algae inside the coral heat up while they produce sugars to nourish the corals after they meat there quota they stop production for the remainder of the day during the night cycle the alge cools down and the extra energy is used for growth. The corals require the same amount in the dark as they had in the light if not growth will be stunted as they will go from grow mode back to producing sugar before they fully cool down
So by running multiple cycles a day you trick the coral in to thanking a day is 6 hrs 3on/3off so you git 3 days of growth for every 24 hrs
