Mag chloride ??

[spawn]

So I went to mix up a gallon of mag today & the mag chloride portion of the mixture has seemingly gained moisture & turned all clumpy in the storage container. I don't get it? The sulphate is fine, so are my ca & alk containers. It's never been any where close to moisture. It is stored in a cool dry dark place @ about 18.5 degrees. I know its not good to use Ca or Alk supps if this happens, but is it ok to use this stuff?