Not IME I was running a uvs 24 hours a day when I had a small gda problem. It made no difference. I lowered my photoperiod a little and it went away. Many others also suggest letting it go through it's life cycle and I will take care of itself.
Yeah, my UV does not seem to prevent (or even kill) algae. I was under the impression that algae would have a more difficult time with one hooked up. In any case, lowering light, increasing Co2, checking dosing amts, are all means of controlling algae. I will say that my water seems a little more clear with the UV, plus I bet it still kills free-floating parasites, etc, if I ever have them in my tank. I guess I can say that after having a UV for 6 months or so, I'm not really sold.
UV sterilizers are meant to kill only free floating algae (ie. green water), bacteria, and parasites. It won't help at all with anything attached to plants. It will help with water clarity, but I've actually gotten better results with purigen. Even if you scrape the glass, most of the algae will have a chance to re-attach itself on the glass and will spread again from there. I only turn mine on when doing water changes to prevent green water, and for a couple days after I add new fish.
turbo, next water change clean the glass with a soft ex foliating sponge or glove, then
run the UV for the first 24 hours while the most algae particulates are still waterborne.
for the rest of the week, be sure to keep your lights on for no more than 8 hours per day.
even one extra hour a day of light can make the difference between having GDA or not.
are you guys with UV that arent having results have your flow rate set correctly? I didnt realize how slow the flow rate had to be when I first hooked mine up, since its inline with my canister its probably only killing the easiest to kill stuff. For example my turbo twist was rated: 253gph for bacteria, 121gph for algae, 55gph for parasites.