UV light kills algae/parasites?

Regarding BGA -- I had a small outbreak of that. I did a 3 day black out and it seemed to get rid of the BGA. Plants not too happy, but they'll recover. Didn't seem to phase the BBA, however...
 
I bought a HOB submariner 5w UV sterilizer for my 40G tank...I had a really bad case of green water and decided that it might be a good investment...it wasnt clearing it as quick as I thought so i did an 80% water change then hooked it back up...in about 3 days or so it cleared it up! As some of these other posters have said it DOES kill beneficial bacteria so I wouldnt run it longer than you need it...IMO mind you
 
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