Cryptocaryon irritans (ICH) - A Must Read For all Marine Aquarists

IMO, the UV can over a long period of time of at least a few months or even longer (I don't know) before all the ICH parasites can be "killed" with your UV working 24/7.

Also, to control the spread:

1) Don't introduce any new ICH carrier into the tank and that's the reason it is important that we quarantine a fish before intro to the main tank for a period of at least 6 weeks.

2) Ich parasites need a host to survive and if there ain't any in the tank; it will take about 6 weeks before you can declare the tank "ich" free.

3) Dose your feed regularly with Vitamins, Garlic-Guard to build up the immune system of the fish.

My 3 cts