It is Morton Brand Water Softener Salt.

your title says deicing salt not water softing salt. I don't know. you would have to check the ingredeints. I know Dr. Foster brand aqaurium salt it only about $2 at many petstore and discount stores. My box lasts a very long time. I have heard of people using kosher salt and pickling salt. Just make sure not to use table salt because it has an anticaking agent in it that is not good for the fish