Eating my coral?

[Frogger]

Your corals that photosynthesize require both nitrogen and phosphorus at a specific ratio to complete the process. If one is limiting the process is stopped or reduced. This will cause the other one to artificially increase because the zooxanthellae, algae and other photosynthesizing organisms don't have enough of the other to continue. Your tank may not have 0 phosphates however any new phosphates that are added via food, additives or fish poop is quickly used up.

This sounds like it is a distinct possibility in your tank. You have enough phosphates to keep the corals alive but not enough to use up the nitrogen or to make your corals happy.

SPS are the most affected because zooxanthellae are their primary source of food.