Can you refrigerate maxibloom feed?

I will be leaving town for about a week and my son is taking care of stuff while I'm gone. He has a busy schedule so I'm trying to streamline everything and make it as simple as possible for him since he's doing me a favor. I have noticed that when I mix up RO water, calmag, and maxibloom in gallon jugs, after a few days, it will get a musty smell to it. I have noticed no adverse effects from it, but I also haven't let them go 8 days. So I'm wondering if I mix a Google gallons up, can I keep them in the refrigerator to help prevent that? I normally keep them next to the tent where it's about 70° and there's a window in that room. Would I be better off just keeping them in a cooler and darker room instead of messing with the fridge? Thanks in advance

Just add some pool shock. No more smell.
If he uses the water right out of the fridge, it would be too cold. The pH will also fluctuate over time in or out of the fridge
What medium? Is he watering everyday or once every couple days?

He would pull the night before using it so I wouldn't worry about the temp. The 2 plants getting it are in soil, so I will be watering today before leaving, that way he can feed in 2 days or so with the feed and then water the next couple times and then I can mix feed up the day I get back. I'd just like to have a little spare on hand in case it's needed. The other plants are in coco but have the blumats and seem to be doing well.

If you're in soil, I'd have him use plain water. They'll be fine.