If you kept the rock wet the whole time, then the bacterial population should be intact. With that assumption, the Ammonia spike is likely from coral dying from being blasted by powerhead and the new lights. Consider reducing powerhead and lighting. Ramp up lights over a week or two.
Any fish? Fish-poop is a terrific source of food for most corals. Phosphate of zero usually results in starved corals.
Any fish? Fish-poop is a terrific source of food for most corals. Phosphate of zero usually results in starved corals.