First you have to figure out why you have the algae. Mine was overfeeding my coral.
If you don't address the why, it will keep growing back.
Here is what I did...
I took out my hairy rock a piece at a time, and using a new brush I scrubbed it and then rinsed it with saltwater.
I used an algae scrapper on the back glass and got all that I could off.
I purchased six emerald crabs, two sally light foot crabs and a blue spotted kole tang. They eat hair algae, so I got them to eat what I may have missed, and as long as the problem is under control they can keep things clean.
It has been a month and so far, so good. I have to feed my algae eaters now because I don't have enough algae for them to eat. I am happy to supplement their diet.
This worked for me so I am passing it along. Like I said..Address the why you got hair algae in the first place.
Good luck, hope this helps.
I just went through the same problem. Decided to buy to bali sea hares they gulp the stuff right up. I had so much though they werent making a dent. I finally decided to take all the rock out and scrup the algea off. It all was worth it cause my rock looks great and my tank is back. Once again i am addicted to the hobby.