Where in the tabk is it located and what fish do you have?
Could be an issue with chem, lighting, water flow or possibley an animal irritating the coral.
Frogspawns typically like med/low water flow but do well in good light. If you have recently changed lighting or adjusted anything in the tank, it may be reacting to that. Even though doing regular water changes you should look into the alk
levels for a possible imbalance. Corals will react negatively if those two have a wide gap.
Do you offer foods to the tank that the corals are able to eat?