Need more info. How old is the tank? What's in the tank? What are your current measurements (specifically nitrates, nitrites, and phosphates...ph too just for good measure)? How many hours a day do you have light on the tank? Also, along with what livestock you have, just how much and how often are you feeding?
Battles with algae are not uncommon, ESPECIALLY in newly assembled tanks...I myself went through a red slime phase followed closely by a nasty green hair phase...solution for me was water change, water change, water change, and reducing the amount of daylight I had hitting the tank.
firefish, ocellaris clown fish
caulastrea, green star polyps, palythoa, zoas