Next time I’m there I’ll make it a point to askWatching the Magic of Disney’s Animal Kingdom?
In one of the episodes, they mention that they have a mixing facility and show it running. Never mentioned which salt was used, but Jay has the inside-aquarium knowledge there.
If you are ever at the aquarium at Disney, you could probably ask cast members, one of them probably would know or could point you to someone who does.
Now you got me curious.