UV sterilizer? when how long?

[FishFun]

I do the same as Stones. I turn it on when I get a new fish then ,if needed, I set my timer to turn on the uv once the tank lights go out, then off when they come back on about 12h on & 12h off. I like the night cycle because the main lights are off & there isnt extra heat added to the water at the same time with lights on. If you get my drift!!!! Thats the only time I use mine is when adding new livestock. I have mine plumbed off my return (dart pump) with a valve to control flow then back to sump.