Those gobies are known to eat SPS polyps and its one of there food in the wild. I dont think he is causing that damge tho. Looks like it got stung or sumthing touch the tips. I have a couple that if I rub with my arm when Im doing something in the tank look the same way a few hrs later but are fine the next day
Clown Gobies don't eat polyps, they are carnivores. When breeding they will chew through the skin of the coral, at the base, to lay eggs on the skeleton.
