sk8r is right on target
I've found that there are more reliable ways to remove algae and phosphate
namely water changes and placing a tang or two in your tank
I removed all my tangs and went tang-free for about 5 months. hair algae exploded. I have pretty good, clean water, too. RO water with routine changes, nitrates under 4. I just [gently] tossed a Kole tang in there to handle the hair algae, and as long as I keep it off the glass, I"m confident he'll take care of the rock.
The reason I got rid of all my tangs was that eventually my tangs were the more aggressive species and my choices for a community reef tank became too lmited.
Kole tangs are known as one of the most docile tangs available, so I made him first. PLUS they're particularly good at hair algae removal.