You have a an unbalanced nutrient issue. What is your NO3
testing at? Feeding schedule? What do you feed? Water changes?
Best way to combat hair algae is to find whatís fueling it, and correct it. Usually feeding too much, not enough export via water changes or filtration, etc. Manually remove as much as you can, do more frequent, or larger, water changes. Feed frozen instead of pellets. All of these will help your issue out.
Just because your corals are open does not mean they are healthy. They could lack color, be reaching, etc. High levels of nutrients are actually growth inhibiting. PO4
will bind onto the alk
/cal and prevent the coral skeletons from growing in a rate at which they should.