What's the rule on pre-mixing fertilizer?

[lotis146]

So I have one of those contraptions you attach to your hose and fill with concentrated solution then spray according to your chosen setting (i.e. 1 tbsp/gal, 1.5 tbsp/gallon, etc). When I first used it I filled the container most of the way but quickly learned I don't use anywhere near that amount on the whole group. Sooooooooo here's where maybe I did the wrong thing...

I put the container in the basement (cool & dark) and then reused the same solution several more times over the course of a month. I'm not seeing any adverse effects that I can really blame on the solution (I'm thinking more that I've got some problems due to way too much rain and my thinking it was okay...). But of course I'm still wondering what's the rule of thumb here; should you only mix what you're going to use right then? Couple weeks?

I'm aware that even if it doesn't go "bad" per se, the mixture is likely more dilute. My question also goes for KelpMax & really anything else you'd put in solution.

Thanks as always! (Shall I admit that this mix also had KelpMax & Inocucor in it?)