I would not have done that at all. Did you search to find where we simply killed the red algae targeted, preserving all the rock portion not invaded
you can target rasp it off, externally like a dentist does to plaque. Place high percent peroxide targeted, on the clean zones it’s exactly like large animal tooth dentistry. Put rock back 99% in tact, target free. Start when invasion is small, right when everyone is telling you the uglies are natural
kudos for no hesitation. Overkill is better than stammering, you hammered it either way.