Cal Hypo caking / clumping

Yes, I use bleach when I can remember to buy it at the store...

But for Cal Hypo, does anyone have any suggestions on keeping a bucket of Cal Hypo from caking / clumping into an unusable mass?

Last time I bought a 25 lb tub of it, and only used about 8 pounds before it got so clumped into a solid chunk of concrete I couldn't use the rest.

Would a "Ziplok" type bag withstand long-term exposure to Cal hypo? If so, I might just portion it out when I buy the bucket and leave the bags in the bucket. I don't care if it clumps in the bag, because then it's a manageable 1 pound chunk.

I'm tired of buying the $3.29/lb "Shock" bags...

Are you keeping it in the original closed container in a dry place?

Yep; original container. I keep it in a garden shed in the back yard. It's out reach of rain & sprinklers, but it's plenty hot...

I have a 22.5 kg (50lb) bucket of HTH with a twist lock lid and it keeps perfectly dry ..is it possible that the humidity is so high where you are that its getting absorbed? Do you leave the cover off while dosing the pool?