I mix a fairly weak kalk solution for my ATO, I usually mix it 1 gallon at a time and add directly to my top off reservoir. Any reason I couldn't make 5 gallons at a time and store it in a jug so I don't have to mix a new solution every few days?
you can and its a good idea the main thing you want to minimize is air mixing into the solution before you use it, so when you pour it or change containers try to minimize the splashing, use a siphon and a tube if you can to reduce bubbles mixing around.