Chicago is 800 miles from the nearest ocean, so when the world’s largest aquarium opened there in 1930, its director decided, logically, that the ocean must come to Chicago. The Shedd Aquarium sent a series of railway tank cars down to Key West, Florida. There, they siphoned up a million gallons of ocean water for Chicago’s “magnificent marble home for fish.” Visitors in the 1930s were greeted by seahorses, sawfish, baby sharks, and a 585-pound manatee.
When the Georgia Aquarium opened in Atlanta in 2005, it too was, for a time, the largest aquarium in the world. (The title now belongs to an aquarium in China.) And it too is an inconvenient distance from the ocean. But in the 75 years since the Shedd opened, aquariums have perfected the science of re-creating ocean water. The Georgia Aquarium didn’t ship any saltwater in from the sea; to this day, it makes its own synthetic version in 80,000-gallon basins.
Today, both the Shedd and Georgia Aquariums use a salt blend called Instant Ocean. You can buy it at the pet store. “We buy one-ton bags, or what we call ‘super-sacks,’” says Eric Hall, the senior director of life-support systems and water quality at the Georgia Aquarium. Instant Ocean is mostly sodium and chloride, the same stuff that makes up table salt. It also contains smaller amounts of other chemicals such as sulfate, magnesium, potassium, calcium, bromide, and strontium.
At the Georgia Aquarium, Hall says that they mix 10 super-sacks at a time in 80,000-gallon mixing basins. They add it to Atlanta’s city tap water, which is first passed through activated carbon to eliminate the chlorine that keeps the water free of dangerous pathogens, but can be deadly to fish. At the bottom of the mixing basins, compressed air shoots out, agitating the mixture as if the water had come to a boil. The Georgia Aquarium mixes up an 80,000-gallon batch about every two weeks.
Working with such big volumes means the aquariums can’t take it for granted that everything will be mixed evenly. When the Shedd first switched over to making synthetic saltwater in the 1970s, it would sometimes find a big lump of undissolved salt in the tank. “We would have to send a diver in there to pull the lump apart,” a curator told the Chicago Tribune. In Chicago, water temperature makes a big difference, too. The city gets its drinking water from Lake Michigan, which can be close to freezing in the wintertime. “It could take a whole 24 hours for it to mix properly and to be nice and crystal clear. In the summertime, it might only take a matter of hours,” says Allen LaPointe, the Shedd’s vice president of environmental quality.
The National Aquarium in Baltimore sits right on the harbor, but it too makes synthetic saltwater for its marine mammals and fish. For one, the harbor water is brackish and not salty enough on its own. And even if the aquarium wanted to add salt to that water, the harbor is pretty polluted. Instead, the National Aquarium makes use of Baltimore tap water and a salt blend called Omega. The aquarium used to make its own salt blend from food-grade individual components. Making it in-house was cheaper, but more labor-intensive, according to Andy Aiken, the National Aquarium’s director of life support. “It also introduced the opportunity to make mistakes,” he says. For instance, forgetting the potassium (just 0.04 percent of seawater) could be disastrous for the fish that depend on it.
Aquariums that can pipe saltwater directly from the ocean do, and Monterey Bay Aquarium, in California, is the prime and enviable example. “Monterey is in this fantastic location,” Aiken gushed to me. “It’s everybody’s dream.” The bay is ringed by protected marine areas, so its water is exceptionally clean. At the back of the aquarium are two intake pipes that supply all the building’s saltwater tanks. “We’re literally physically connected to the bay,” says Kasie Regnier, the director of applied research at Monterey Bay Aquarium. The pipes can bring in almost 2,000 gallons of water a minute.
It works out great, except for the jellyfish problem. In certain years when the conditions are right, big swarms of jellyfish will appear in the bay. “They get sucked onto the screen. They’ll crush our screens,” says Regnier. The aquarium actually has to send divers down to unclog the intake pipes’ screens of jellyfish. (The divers, for their part, have gotten stung in the face.)
The bay water is clean, but it’s not clear like tap water. “The ocean isn’t crystal clear,” Regnier points out. It’s full of organic material and living creatures such as plankton. But cloudy water also makes it hard to see inside tanks. So running an aquarium means finding a balance between satisfying visitors coming to see creatures and the health of the creatures they’re coming to see. Monterey strikes this balance by running raw seawater with all its organic material at night, and then switching over to clear, filtered seawater in the morning. “Clear doesn’t mean healthy and clean doesn’t mean healthy,” says Regnier.
The aquariums that make synthetic seawater are also paying attention to microbes in their water. In 2008, the Shedd Aquarium started piping reclaimed water from marine fish tanks into its marine-mammal habitats, and its scientists noticed a trend: Microbial diversity went up in the mammal habitats, and infection rates actually went down.
Historically, aquariums thought the fewer microbes, the better. Bacteria counts in marine-mammal pools are strictly regulated by the USDA, says Chrissy Cabay, the director of the Shedd Aquarium Microbiome Project. But maybe there is such a thing as too clean for dolphins. Maybe a healthy microbial community can prevent nasty pathogens from taking hold—as we’re seeing in human health. This research is still in its early days for marine animals, says Cabay, but the aquariums are getting interested in the microbiomes of their habitats.
In 1930, as the Shedd was using railroad cars to bring saltwater to Chicago from Florida, The New York Times explained to its readers why the undertaking was necessary: “Synthetic seawater, it is said, would not do at all; for what is needed to keep the fish in condition is such organic matter as is available only in their natural environment.” Nearly a century later, aquariums have figured out how to keep fish alive in synthetic seawater. But analyzing all that “organic matter” is still a work in progress.