Whitjr,
I think you will really like that sprayer. Especially with the disassemble feature at the wand/nozzle.
I have one that holds 3 gal. and usually fill it to two gal. If things are nearby, three gal. is real doable. ... Just a small tip here: I have a deck around part of my cabin, and I set the sprayer at mid-back height on that deck. I fill and mix right there, then I just step down on to the ground, and back right up to the shoulder straps. It slips right on real easy at that height, and I simply walk away with it.
I used it with Round Up this past summer, and did mass murder on a bunch of white snakeroot.
I have never used Nutri-grow, but I did clean out my sprayer really well, and treated my soil with an extremely mild dosage (1 tbsp/gal) of epsom salts. I did that after my soil test late last spring. I will do a re-test late winter 2012. The sprayer worked really slick for that application. A nice even mist. The one I have requires almost constant pumping, for even misting, but with the pump handle on the left, it is not bothersome at all.
I wonder if somehow a person could come up with a calcium mix? ... Dunno.
Bill