Sorry. That ich treatment doesn't work, and the fish if that bad that fast is in trouble. Get him into qt with treatment asap. Ich is not about stress. It's an animal like fleas. You need to de-flea the fish, and set up a tank where you can treat him. A bare 10 gallon tank with anti-jump protection, a filter, and heater are all you need. Even a 5 gallon bucket. Alternate bucket and tank with filter, according to the instructions in the TTM sticky and you may save your fish. In any reckoning, no fish should enter that dt for 72 days. As well as keeping salinity steady, watch your alkalinity: it is a prime culprit in fish that suddenly succumb to ich which they may previously have dodged, because if alk sinks below 7.9 it can affect a fish's slime coat, its protection against this sort of pest. It's a sure bet your dt is now infested, and nothing will go well until you starve the pest out.
