Is yours a reddish-purplish color? I just have a tiny amount growing out of the base of one of my hammers. I sure didn't see it when I put that in my tank, but it's growing now. I have not seen any other spots in the tank where it grows, but it doesn't seem to need a lot of light as it's growing underneath the hammers and you can only see it right when the lights come on or with a flashlight at night. So, it could be somewhere else where I cannot see and I wouldn't know. If it is algae, my tangs don't seem to be interested in it and they'll eat just about anything plant wise. Hopefully someone will stumble across this thread and point us in the right direction.