I noticed when my lights are off my tank has a slight green foggy tint to it. I have a UV sterilizer from another tank that I just put in my sump and set up for 3hrs a day.
Is there any downside to using a uv sterilizer in a reef tank? I have it like this at the moment.
I think someone else posted about the damage to plastic (tanks frame) from UV like the one you have. Good ones have an enclosed area to keep the light from burning everything, those are dangerous to your eyes too.
Otherwise, 3 hours a day will not kill the algae in the tank but it might kill the tank and take the algae with it.