Please read the links Mike posted above.
If you want to be "ich free" you must:
1- take all fish out of your tank and treat them for ich with either a copper treatment or hypo
2- leave your tank fishless for 6-8 weeks. Ich is a parasite that needs a host (fish) to live off. It will die off if there are no fish in the tank for it to feed off.
unit will only kill what passes thru it. The chances of every parasite making it to the UV
is slim to none.
Temp will not bring on ich. The fish either has it or it doesn't. If you have a fish that was treated and cure of ich, it will not get it again unless it's (ich) introduced by another fish.