As said, UV's are great and useful when sized and run properly. Most people get ones that are way to small and run way to much water through them making them pretty much useless. I also see a lot of UV's either on the main return line getting too much flow, or short cycling in the sump where its tapped off the return and goes back to the sump then right back to the UV.
If you want one for algea/diatom control, dont bother. Fix why you have algea first.
If you want it for parasite and infection control, make sure its sized right. I simply would not bother with anything under 40w because its kill ich flow is around 100 GPH and I wouldnt use it for anything larger than 150 gallon tank. For example my 540g system has a 150w UV that must be run at 450 GPH or less to kill ich. Thats barely turning over the tank once an hour, which isnt much.
It is a fantastic tool to use, and I would not run a tank without one. But if its not done right, its just expensive and useless.
Also can someone resticky the UV sizing thread? Thats a great one.
