Ich established tank

[moondoggy4]

No new arrivals, 3rd party thermostat went out on my heater early cool weather nights to 43 degrees, temp got down to the low 70's DT for 2 days early morning temps. PBT have for 7 years, now has ich it is starting to **** him off, no other fish seem to be affected.

Any thoughts or suggestions? He is about the size of my hand. I do have a 20 gallon QT going with two fish 5 fish in there right now.