UV cannot cure an ich infestation. UV is good with algae, which is why pondkeepers love it; but parasite control is something else. It may help, but ich control requires 100% eradication, which is impossible with UV. IMO, it often does more harm than good by providing a false sense of security and delaying real treatment.
Not to get off topic but everything you wrote is for the most part not true. Most people do not use the correct wattage or flow rate to effectively eradicate parasites with an UV sterilizer.