1. Always store powder nutes of any kind in an airtight container. I like 5 gallon black buckets with gamma seal lids(on amazon).
2. Always store said containers in a controlled environment. Obviously high humidity being the biggest issue.
This brings up a question of mine. First thing I did was buy lowes buckets with lids when I moved to dry ferts. This is because I left open a bag of MG and it turned a whitish color? Not very translucent anymore. The thought crossed my mind it was possibly changed chemically due to exposure. Is that bag of MG bunk or can you still use it?
After reading this I am also going to add a good bit of the color sense desiccant I have to the buckets just for good measure.