FTBC - I had heard the same thing about the blocks so when I need another, I opted for the blue free running salt. I figured it couldn't hurt to try it in another form. I forget why I bought the blue instead of white now... There was a reason, but that was a couple of years ago. LOL It could even be that the white was not available. Small towns. <sigh>
I keep the salt in the barn, sheltered from weather and my mare has free access to it.
The salt that is in my storage pail is even packed a bit. We are not in an overly humid environment, but even our road salt gets packed in its container.