The thing I was worried about with premixing it in one gallon, and adding it in....I think that would throw the ph off. You would have ph'd the one gallon solution....things would most likely be different when you add it into the big rez....and when the ph is off in the solution, strange things happen to all of the suspended salts and other matter in there.....I know...not real scientific...but I'm a stoner, not a scientist!