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That is a broad question. What is the flow rate through the UV? Why are you using it? For protozoa (ich) or for clean water? If it is slow flow rate for ich any codepods in water that runs through the UV will die. You will still cultivate the codepods in the sump etc.
Answer is easy to find. What brand UV is it? How many watts? What pump are you using? Is it connected to you return line?
If it makes you feel better, I have a 260 Watt UV and everything goes through it before it reaches my DT. Does it kill pods and bacteria? Hell yes, but the bacteria and pods are cultivated in LR , Sump, Fuge etc.