Mag chloride ??

[Chin_Lee]

Yes it is still safe to use. Its no different if you were to add water to them now or if they had absorbed the water from the air before.
Many of these chemicals (Calcium and magnesium mixes) are desicants to a degree in that they will absorb any moisture in the air. Just makes it hard to weigh/measure them.
I just recently found out that Dri-Air (the stuff you put into RV's and marine boats to take the moisture out of the air during storage) is just Calcium Chloride.

[eli@fijireefrock.com]

If you product is near moisture high area or letf open for even a small period of time it will pick moister like a sponge.
The best way to do the calculation for any recipe is if you originally know how much weight you had prior to moister or original weight and how many batches you had done out of that specific container and where did you get the chemical as this will change your recipe.I have no problem fiding out for you as to how to use simply not to nuke your tank.let me know.

[whatcaneyedo]

Yup that is how my Magnesium Chloride is too. Its so bad that I have to use a chisel and mallet to get any of it out of the pail.

[hillegom]

Mine is dry as a bone, still flows even after a year now.
Tightly fitting lids is the cure. ie, when the salts are new.
From my high school chem, I remember the name hygroscopic
That was a looooong time ago