I have this also. I was told this is caused by not enough surface tension breakage, causing a deplesion of oxygen in the water. I was told there is something you can use to combat this crap. Nothing will eat it.
Usually it can be removed by pulling it out as a whole mat, if necessary, make a bath of salt water, perhaps a five gallon bucket or so, and gently abrade the surface to remove as much as possible...there are several brands of red algae killer on the market, but have no info on whether or not they are harmful to cephs....
What ever you do, do not stir it up
It is a constant battle until you take care of the problem.
I remember whe I first started out, a long time ago,
You had 4 stages of a marine tank, and everyone went thru it
0. Set-up the new tank
1. Diatom algea (eating all the stuff in you new water)
2. Hair algea (eating the decaying diatoms)
3. Cyano (eating the decaying hair algea)
4. Mature aquarium
These steps have become almost unoticable with RO water,
but they are still there.
Out here, with our funky water, it seems to be silicates that cause the red algae bloom...good call, Colin.
Yep, KIA is correct too...you don't want to get it all over the tank, if you do need to brush the live rock, do it in a seperate bucket, and then get rid of the offending water!