I can't help myself. As others have said need to know more details, but here is the combo to hit it with:
Better skimming (clean, possibly upgrade) and feed less to lower nitrates
Use RO/DI water and check the TDS
Throw some GFO (PhosBan, PhosPure, etc) in a high flow area
Shorten the light cycle by a couple hours
Add a fuge or some "safe" plants to the tank
Add a nice variety of snails
Finally, remove the existing algae
One or more of those should squelch the algae.