My guess is its red bugs that i still havent treated and its been about a month sense i noticed i had them.I would frag what is still healthy being clear to frag only what is healthy so you may end up leaving some on the colony that has color and polyp extension. Any thoughts as to what is going on? Has anything changed with your systems? Are the params in line?
i know it did also have hair algae start to grow on it i tryed to blow it off but it kept coming back?Cut and make sure you remove well above the necrosis. If you have redbugs I would treat sooner than later. However, it's doubtful that they were responsible for taking out a colony in a few days.