Actually its hard to believe but seaworld does use IO for its salt water.
"Most public aquariums located inland use artificial seawater. Among these are Sea World at Orlando, Florida and the John G. Shedd Aquarium at Chicago, Illinois. Formerly, the latter used natural seawater held in reservoirs with a total capacity of 1 million gallons. These reservoirs were replenished periodically by natural seawater brought up the Mississippi River by barge from the open waters of the Gulf of Mexico. With the rising costs of transportation, however, it became more economical for the Shedd Aquarium to make its own seawater by adding 31 tons of salt (with trace elements added) to every 285,000 gallons of freshwater. An electric mixer is used for mixing 600 gallons at a time in a special tank; then the mixture is transferred by hose to the large reservoirs."[/quote]