|Is there a high or low temperature precaution concerning Potassium permanganate?
Potassium permanganate is a superb remedy at any water temperature below 80 DF however - even above 80 DF it can be used with caution and ample aeration, you just have to be more careful.
As cold water remedies go, none is as good as potassium because the colder the water, the safer it is. Better still, most medications rely on the progress of the parasite life cycle, such as salt, dimilin, malachite. Potassium doesn't. It kills the parasite whether it's metabolically active or not.
So treat ahead. It's safe in very cold water. Just DOUBLE check all doses and amounts. Have your spouse review your math. Whatever it takes, because people kill fish.