Welcome to the forum Platy Freak.
Ich treatment is a must regardless of the fish that are present. Ich is cured by killing the free swimming form of the parasite. The parasite simply grows on a fish or invert for a while and once it has developed far enough it drops off to continue its life cycle. A couple of days on the tank bottom and it becomes free swimming and starts searching for a new host. At that stage only, we can kill it. If you have treated a tank long enough for all of the parasites to go through the life cycle, you will never see another parasite in that tank. I have a link in my signature area that will help you understand the life cycle in more detail but the simplest way I can say it is to say that the parasite arrives living on something and can be killed easily before it harms your fish if you treat as soon as you discover it. A very common error is to try to minimize the harm to fish or inverts by reducing the treatment or the treatment period to a value not quite good enough to remove all of the parasites. Anything short of a full eradication will mean that your fish get re-infested by those parasites.
Please take the time to follow my link and really become an "expert" on ich. I killed many fish when I was younger by trying to spare my fish being exposed to more medication than I thought they really needed. The second or third appearance of ich made me think there was something wrong with the treatments I was using and sometimes claimed the life of my fish.
A clean looking tank is not necessarily one devoid of ich. Ich arrives as a parasite on fish or even plants that are introduced to a tank. If you quarantine all new fish for a couple of weeks, you will never see ich in your main tank. If you do not, as I often don't, you may need to deal with ich on occasion. Simply said, ich can exist on fish as a single spot that may even be inside the gill covers. Nobody can spot every infestation 100% of the time so quarantine is a way to safeguard your main tank.
