uv is usually used to treat bacterial blooms (white cloudy water) or water borne fish diseases/virus that may exist.
if th tank isnt by a light (like how monocus mentioned) its probably an issue with the tank recieving light 100% of the time. i am guessing its in a well lite hallway with regular florescent blulbs which is great for algae growth. This probably isnt possible but if there is a social room or something that actually gets dark at night i would ask to move the tank there or this will constantly be an issue.
Maybe someone on here could give you an old phosban reactor as well. GFO (granular ferric oxide) will help more than UV would. If i had a spare i would ship it to you but i dont, sorry
