Update: No more hair algae at all, and the problem has been solved. I took out all of the rock and scrubbed it in salt water. Actually when doing a water change, I used all of the old water to do the scrubbing of the rock and put the rock back in the tank with the make-up water. Next I stopped adding frozen mysis shrimp directly to the tank. Then I added a couple of snails, emerald crabs, and a sea hare to my reef. I know the hair algae problem came from the frozen mysis shrimp, it is like rocket fuel for any algae to grow. Thank you everyone for your help.