Aside from the question, "UV or not UV" . . .

Does the UV source go on your pump outlet line, so that all of the pond
water passes through it?

I see 'clarifiers' of about 7 Watts, for a 1500 gallon pond, and
'sterilizers' of about 40 Watts for a 1500 gallon pond. What's the diff?

Seems like it would reduce the pump flow if you run it in-line with the pump
outlet - is this a problem?

Thanks!