tank size, filtration, ferts used, fish/inverts in tank, ect... If something else isn't a major problem causeing the hair algae growth. ime a pair of long finned rosy barbs do a good job of handling hair algae. I say a pair as they will tend to deal out their aggression on eachother and not tankmates.. and long finneds ime tend to be much more docile then the short finned variety.