ich is introduced by not putting everything wet through a qt process!! it is a parasite...if you don't introduce it into your system, it will not be in there!!!! if you qt EVERYTHING WET, and watch very closely for 4-6 weeks and don't see any sign of it, it is pretty safe to say that it is not present...some people like to treat for it anyway, just to be sure..a stressed fish cannot get ich if it is not present in your tank...don't ever believe anything that you hear about ich being a stress related disease !!!!! it is a parasite...if the parasite is present, it can manifest itself on a stressed fish faster than a healthy fish..this doesn't mean that a healthy fish cannot get the parasite..you cannot really control it without treating with hypo or copper, but there are a few things that you can do to try to boost a fish's immune system...you can add vitamins and garlic to its food, run a u.V sterilizer, and keep the water quality as high as possible..this will by no mkeans keep the fish from getting the parasite, but some people like to keep the immune system as high as possible, "in hopes" of beating the parasite