Brine Mixing

Hello, I’m using rock salt to mix into the tanks of units so they do not freeze. The Johntalks recommends 1/2 lb per gallon, but does that only cover the 5 initial gallons of chemical we add in? If its a 50 gallon tank, should I mix in 25 lbs? Because that will be way over the euetic point for the initial 5 gallons. Sorry its such as silly question