I have been storing water crystals in a cranberry juice container that I cleaned out, but after about 2-3 weeks its starting to smell mildewy. I know I cleaned it out well, but am thinking its from me trying to be a smarty pants and adding a little Tang drink mix to entice my roaches to use it. I have been refrigerating it, but there was a day where I accidentally left it out for half the day.

Ive dumped it out, and won't be using that batch for my roaches to be on the safe side. But is it from the Tang, or should I be refrigerating smaller batches because this can happen even with water crystals with nothing added?