black algae on live rock

Hi ...

I have a 20g microreef in the office. There's a black
algae coating the live rock that's difficult to remove.
It gets into the pores. It's a thin layer and does not
seem slimy. I try to brush it off but it always grows
back.

Are there snails or other critters that will eat stuff
like that? I'm also trying to grow coralline algae so
I've been avoiding algae grazers.

The rest of the tank is otherwise healthy.
Here's the specs:
- 20g long microreef
- powerhead and filter for circulation
- Red Sea skimmer
- 2 cool white, one actinic flourescent lights, 3w/gal
- 3 peppermint shrimp
- few corals, all doing well (xenia, hammer, couple of
gorgonians, small brain, few mushrooms, green star
polyps, button polyps), 3 peppermint shrimp, and some
caulerpa.
- No fish.
- corals are fed small amounts of phytoplex and
Microvert (both by Kent Marine) once every 2 days
- started doing water changes more regularly, about
2 gal. every week.
- dose calcium, strontium, iodine, molybdenum, and
trace (coral-vite) every week.

thanks,
shireen


--
Shireen Gonzaga, Data Analyst, Space Telescope Science Inst. O-
3700 San Martin Dr., Baltimore, MD 21212, USA. _/ )
Office tel.#: 410-338-4412, e-mail: /|