I think it’s is just a bad pot...I Imagin it was a bad fire job or something in the clay reacting to the water. I have a few of these pots from the same seller and this is the only one that whitens up.
Most likely will just have to see if the salts stop pushing at some point.
Bummer.... I really like this pot!
It might be a bad idea, but when I was living in a shitty apartment with some busted floor tiles in the shower I used dollar store silicone spray (the stuff used to keep ice/rust from building up in your car lock) to make the floor repel water.
As far as I know, the floor is still holding up and it's still water proof.
I don't know how the pot, nor the tree would react to that though. I imagine the clay would turn a few shades darker. But it might be a preventative solution for someone.
A more diluted version of the stuff is used to waterproof hiking shoes and tents. No water means no mineral build up!