Algae can and will still form on surfaces, even with a UV sterilizer running 24/7. I notice it in my 55 gallon, in places where my plec cannot reach. I don't even know if there is less algae on surfaces do to the UV filter, since I have no way of confirming it. (no tank set up in the same place, with the same stock, same lights, etc. - sa many variables to consider for a meaningful answer)