|Should I keep the salt level high with all of the weather changes (hot days....cold nights)?
Salt operates almost exclusively (without regard to) any fluctuation in temperature. I have used salt hundreds of times in icy water, and very warm water.
Since most treatments are naturally being applied to sick fish, you should be very aware that ANY fish with gill trouble is going to have a harder time breathing in warmer water (over eighty degrees fahrenheit) because warmer water carries MUCH less oxygen than cooler water. The perfect tmperature for fish whether they are healthy or not, is seventy four degrees Fahrenheit.