"George Patterson" wrote in message news:i96nf.14686$OK6.1492@trnddc03...
I would not say you *need* one, but I've kept at least one on my tank for about
30 years. It seems to reduce the number and severity of outbreaks of parasites
like ick.

Have you kept a comparable setup without UV for 30 years to say
the one with UV has reduced number and severity of outbreaks of parasites?

In other words, my question would be:
you claim it has reduced number and severity
of outbreaks compared to what number and what severity ?