Rubbed the brown off a coral?!

[TheDeepSandBed]

So I have been dealing with some hair algae that is growing in my tank. While doing so I took a toothbrush and GENTLY rubbed a coral (acro) to get some clingers and it looked like some of the brown came off! The coral looks a little bleached in the area I rubbed. Can anyone explain what is happening and if in the future I should avoid this at all costs?

 

[Eastone]

you may have damaged the skin/skeleton. I'd not worry too much, I end up doing the same to a few coral tips every time I clean mine