well, you dont always see the parasite when its on a host, you can only see the parasite when its "pregnant". I personally had a kole tang, one of my favorite fish, and it died from ich. I waited too long to qt it and didnt have a sterilizer. Since i have gotten my sterilizer, i havent lost one fish to ich, and I own a scribbled rabbitfish, purple tang, blue hippo tang, powderbrown tang, and a moorish idol which I've had for over a year now. The decision is your call, but if it were me, the only way i wouldnt do something about it is if you have any fish susceptible to the parasite. The fish that can usually live through ich breakouts are hawkfish, blennies, gobies, dragonets, sometimes damsels, clownfish, basslets, cardinals,etc. Many people recommend removing all of the fish and treating copper on them, which ich cannot live through a copper or hypo treatment thus killing any ich on the fish. And then you basically starve the ich remaining in the fish tank to death by removing their food source. Its your call, a UV sterilizer is a pricy investment, I paid close to 250.00 for mine, but I've realized after so many fish dying on me from ich that not only was I losing money, but losing things that i was getting attached to also. Your call, but in my perspective im a firm believer behind the UV sterilizer because out of the 3 methods(UV sterilizer, fallowing the tank, leaving it alone) which I have tried all 3, the only one that has worked for me is the UV sterilizer, and it worked with flying colors. some dont like it because it kills any micro organism that flows through it like pods and phytoplankton, but personally i have 2 dragonets, a mandarin and scooter, had them for over a year and they are doing great, and i have never added pods to my tank, and i have corals that do just fine. Your call.