brown circle/patch on my live rock

[Jack]

I bought the samerock you did, at the same time, from J&L. I do have these brown spots too in sections on my rock, I think it is a wierd colour of coralline algae but I'm not sure on that. I don't see it being anything bad. I don't percieve this as a plauge or problem to me, and it's doesnt seem to spread I don't think.