Hello and welcome to RS
It is important to carefully hand pluck as many as possible and remove them from the tank at least once a week but the more often, the better. Make sure the nitrAtes are low (10ppm or less) and the po4 is low or undectible. Regular water changes, an ro/di filter, a good skimmer and phosphate media will keep the nutrients low and help to starve out the algae.
Good luck and don't give up the battle!