sea salt

I am in Istanbul, Turkey. I started this hobby in 2006. I have had many aquariums in fresh and salt water. The latest one is this one with dimensions of 100x60x45h cm. Greetings everyone.

I'm just curious about sea salt. I'd like to know more in depth of why it's not good to use sea salt that has moisture in it to use it in a fish tank. I'm a little confused because it gets wet/ dissolved into our aquariums and I'm pretty sure alot of salt on the market comes right out of a wet...