UV light

Only free floating algal species, such as those that cause green water.

please correct me if im wrong
but wouldnt a uv sterilizer kill other algae spores
or gsa that was razored off glass and being drawn in sterilizer instead of reproducing

Of course. Any free floating spores/algae that has been scraped off that makes it way though the UV sterilizer will likely be killed as well, but that is more incidental.

UV is very good to kill algae.