Do UV sterilizers substantially reduce risk associated with adding new fish
without quarantining them first?

I would say yes, because IME, the main risk is ich, and UV sterilizers are
effective against ich. Not sure how effective they are against bacterial or
viral diseases, but those usually aren't much of a problem if your fish are
healthy.

What are the implications for plant
nutrients? I hear the UV energy can oxidize, and a presume render
plant-unusable, some key nutrients. Is this a manageable problem?

The effect is minor. Hydroponics growers use UV sterilizers all the time, and
they don't have any problem.




Leigh

http://www.fortunecity.com/lavender/halloween/881/