I am new in UV sterilization. I run my unit 24/7. There are a lot of myths regarding the use of UV. There's no sound reason not to run it around the clock (just replace the lamp every 6 mo and at that time cleaning the quartz sleeve -if it has one), other than only if you are starting to cycle the tank, and even then, I don't think it will make any difference. Different pump flow rates are recommended for the multiple uses of UV.
Please check this article on UV, I found it very informative and honest about UV use in fishkeeping:
http://www.americanaquariumproducts....ilization.html
Pepe
Santo Domingo
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