Personally, I don't store it - I'd rather mix a fresh batch every time I give it to my plants so I always try to figure out how much they're going to use and mix that. If I've mixed a little bit too much, well, it runs out the bottom of the pot and that's ok with me. When you talking about a small grow - a couple of plants - as opposed to an entire room full of them, then that's easiest to do AND safest... you'll know your plants are getting the best nutes they can have.
Good luck...