Elevated nitrates and phosphates cause nuissance algae. Identifying the source of the problem works best -- overfeeding, overstocking, contaminated water source, etc. In the meantime, manually removing the algae does help (even though it seems like a never ending battle).
If phosphates are a part of the problem, running a phosphate removing media can help, but correcting the source of the phosphates tends to be cheaper in the long run.
If your lights are on too long, that can make the problem worse. Cutting back on the photoperiod can also help while working to correct the source of the issue.