Reefers, as coral reef keepers sometimes call themselves, browsed through wares like Ultra Blasto coral, which looks like a head of psychedelic broccoli. A Katherine's Fairy Wrasse supermale fish, a torpedo of orange and white, could be yours for $150.

Thanks to recent advances in aquarium technology, you, too, can grow a coral reef in your basement. The best of these aquariums look like sections of the sea floor that were spirited away from the ocean: Fish dart above anemones. Coral polyps unfold like cherry blossoms.

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But sometimes, the coral attacks.

If provoked, certain zoanthid corals, a relative of sea anemones, erupt with one of the most potent toxins ever discovered.

In May, members of a family living in a suburb of Adelaide, Australia, scrubbed the coral tank in their home and went to bed. A few hours later they awoke, struggling for air. The family was “quite unwell with breathing difficulties,” said Daniel Hamilton, a spokesman for the South Australian Country Fire Service. All of seven members of the household were hospitalized, the youngest child in the intensive care unit.

Within an hour, Hamilton said, emergency responders traced the incident to the scrubbed coral. The animal reacted to the cleaner as though it were a predator, spewing a chemical that spread through the house as an aerosol.

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Officials on the scene quarantined the building. “This isn’t the sort of thing we’ve dealt with before,” Hamilton said. It took three hazmat removal groups wearing breathing apparatuses and suits to clean up the mess, Australian newspaper ABC reported. They neutralized the toxin with bleach and vacuumed up the particles.

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Corals sold for home aquariums have not been comprehensively tested for toxins, said Jonathan Deeds, a Food and Drug Administration scientist. “We know not all species can produce toxins but at least several species can in high amounts.”

The most dangerous chemical compound released by coral is called a palytoxin. It burns skin and eyes on contact, and if it gets into the air, the chemical can wreak havoc on throats and lungs.

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Such poisonings are rare. “I don’t want to create panic,” said Aurelia Tubaro, a toxicologist at the University of Trieste in Italy. That said, she considers the risk of palytoxin poisonings to be underestimated. “We have to inform people.”

The danger of inhaling palytoxin is relatively new. Before the 1980s, most home aquariums could keep fish alive, but little else. People bought dead corals as curios, valued for their ornate skeletons but not as living critters.

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Andrew Rhyne, a marine biology professor at Roger Williams University in Rhode Island who studies the trade in exotic fish and aquatic life, said, “To understand the trade in corals you have to understand marine aquariums in general: It is mostly technology- based.”

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Mimicking the equatorial sun indoors posed a huge technological hurdle. The first metal-halide lighting systems generated so much heat that, to disperse it, aquariums had to be “really, really big,” Rhyne said. A switch to cooler, more-energy efficient lighting — to fluorescent bulbs and then to LED lights — gave way to more manageable tanks. And then a coral hobby boom.

From 1990 and into the mid-2000s, as Rhyne and his colleagues reported in 2012 in the journal Conservation Letters, the importing of live stony corals into the United States grew by about 8 percent per year. The 2003 film “Finding Nemo” triggered a spike in pet clownfish and anemones. Based on data from the Convention on International Trade in Endangered Species treaty, the biologists traced a peak to 2005, when importers reported roughly 600,000 pieces of live coral brought into the United States. The 2008 financial crisis, plus a rise in aquaculture and farm-raised coral, reduced later demand for imports.

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As the hobby grew, reefers flocked to the Internet to exchange information. In the early days of the Web, Rhyne said, aquarium forums were “literally some of the highest- trafficked” sites. Indoor reefs have many churning parts — wave-making pumps, artificial lights, janitor shrimp — that keep collapse at bay. An invasive pest or sudden change in pH can bring mass die-offs.

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“The sharing of information has really helped,” said John Coppolino, a 39-year-old engineer and hobbyist who designed his house in Virginia to accommodate his massive 1,300-gallon tank. “Guys at the tip of the spear, like me, make it much easier for guys like you who are not in the hobby.”

Rhyne likened the best hobbyists to master gardeners. “It's amazing what they’re growing in their basement,” he said. As gardeners trade rare orchids, the reefers exchange fragments, or frags, of coral among themselves.

If anyone at the Reef-A-Palooza event in June seemed troubled by existence of toxic coral, they kept it to themselves. Although a few sellers used tongs to lift their wares out of tanks, several coral-mongers simply picked up coral nubs with their fingers. Or hefted entire, polyp-encrusted rocks with bare hands.

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Veteran hobbyists know about the danger. In 2015, a Reef-A-Palooza in Orlando hosted a lecture on palytoxin, and websites aimed at aquarium owners post well-informed alerts. Aquarium shops raise flags, too; one store in Anchorage displayed “many signs warning that some coral might be very toxic,” according to a 2015 case report.

When asked if he was familiar with the toxin, Philippe Gilbert, owner of the Canadian coral nutrition company Polyplab, said, “Yeah, of course.” People who have spent time in the hobby, he said, have heard the horror stories.

He said the biggest problem is when “people are misinformed and don't know what they're doing.” In some of the worst cases, hobbyists have boiled infested rocks to kill unwanted coral, which can trigger a toxic response from Palythoa species. But according to scientists like Tubaro, even experienced aquarium shop owners have gotten sick from their own coral.

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One hobbyist at the online Reef Central forum issued a warning in 2003: “I wanted everyone to know that Zoanthids are very toxic,” he wrote. His dog stuck its head in a tub of coral, and the poor pooch died a few hours later.

In 2005, a reefer named who goes by the name Steveoutlaw wrote on Reef Central that an ugly green zoanthid appeared in his tank. To stop the spread, he dropped the infested rock in boiling water. In its dying moments, the coral released the toxin in a plume of steam. Steveoutlaw inhaled the vapor. What began as a runny nose gave way to “coughing fits that would make a grown man cry,” he said. He went to the emergency room and was later released, though asthmalike symptoms persisted.

Palytoxin is an unusual poison, and incredibly potent. It is a huge organic compound, technically classified as a fatty alcohol, that disrupts a molecular pump found in cell membranes. The pump maintains the balance of sodium and potassium ions within a cell. Palytoxin jams the pump, throwing ion ratios out of whack. “This sustained ionic imbalance condition leads to cell death,” Tubaro said.

Luckily, there are no records of anyone dying from palytoxin inhalation. Breathing the toxin leads to high fever, conjunctivitis, difficulty breathing, cough and a runny nose, per Carmela Dell'Aversano, an organic chemistry professor at the University of Naples Federico II in Italy. Neurological effects include vomiting and vertigo, she said, “and the sensation of cold at the extremities.”

“People in my lab have developed problems in the eyes” from working with the toxin, Tubaro said.

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A pair of chemists discovered palytoxin decades ago when they followed the tale of "Limu-make-o-Hana," a Hawaiian legend that roughly translates as “deadly seaweed of Hana.” The myth involves a sinister figure who has a shark mouth. A textbook on marine toxins cites the 19th-century Hawaiian historian Davida Malo: The figure was a shark god, and a toothy maw grew between his shoulders.

This god was not kind. He slew anyone who entered his fishing spot. But he was mortal. A group of rival fishermen killed the god, and they burned his body and sprinkled the ashes in a tidal pool. Warriors who dipped their spears in tidal pool ensured their blows would be fatal. Poisonous seaweed grew in this contaminated water, the Maui locals said.

In 1961, Philip Helfrich, a professor at the University of Hawaii on Oahu, and a graduate student named John Shupe, persuaded fishermen to take them to the tidal pool in the legend. There they found, not seaweed, but a species of anemone, which they named Palythoa toxica.

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Within a decade, chemists identified the macromolecule, naming it palytoxin after the soft coral species. But it would take decades of work to understand palytoxin's structure. “If there is a Mount Everest of chemistry, it has to be palytoxin,” began a 1989 article in Chemical & Engineering News; that year, Harvard chemists finally worked out its massive shape.

There was a flurry of interest in palytoxin's potential for killing cancer cells in the late 1980s and early 1990s. Writing in the Scientist magazine in 1990, journalist Paul McCarthy entertained the notion that, “palytoxin may be mounted on antibodies instead of spears for use as an immunotoxin in attacking cancer cells.”

It can also be a dangerous food contaminant. In the span of a week in 2000, 11 people who ate fish in Japan were treated for palytoxin exposure. In some instances their urine turned black. The toxin was also implicated in the death of an East Timorese man who became sick after eating a tainted crab.

Such illnesses present a puzzle. Algae, not Palythoa corals, contaminated the food. “The palytoxin group of toxins are found in many organisms,” Dell'Aversano said. There are about 30 different toxins with the same chemical spine, though the atoms stuck to the backbone may differ in places. “The real origin of the toxin is still controversial.”

A few bacteria produce palytoxin-like compounds, Tubaro said, and it is possible that the algae and corals harbor these germs. Another hypothesis is that toxic algae live in symbiosis with Palythoa. But “the actual culprit,” she said, remains to be found.

In 2005, an algae named Ostreopsis ovata bloomed in the Mediterranean Sea. Hundreds of people near Genoa, Italy, became ill when the breeze blew a palytoxin-like chemical at beachgoers. About 200 people sought treatment. In the wake of the hospitalizations, tourists steered clear of the beach. (A year later, the mayor of Genoa was caught splashing in the water, shouting at passersby that the sea was safe. Nobody took him up on the offer to get in, the Guardian reported at the time.)

In the wake of the bloom, Italian researchers including Tubaro and Dell'Aversano set their sights on palytoxin. Then, in 2008, German researchers published the first report of a hobbyist who was injured after touching coral. Medical reports of reefers who inhaled the stuff followed afterward.

It is not easy to gauge incidence from the literature, Dell'Aversano said. In a 2014 paper, she and her colleagues counted 47 cases of poisonings. “It was quite hard to find the data,” she said. “Sometimes the reports are anecdotal. They are not reported in scientific journals.” Nor is there an incentive to publish a report for every medical case, she pointed out.

Tubaro said she receives phone calls from colleagues once or twice a week about possible palytoxin poisonings. The day before Tubaro spoke to The Washington Post, she said she had been sent a photo of the injured eye of an aquarium store owner.

In 2011, FDA scientists, writing in the journal PLOS One, reported it was possible to purchase toxic coral in aquarium shops near Washington, D.C. (Deeds bought one Palythoa cluster for $5.) The CITES treaty regulates the international coral trade, but there is no law against selling any particular species of coral within the United States.

Palythoa corals can end up in tanks even if they were not purchased. “In our experience, most of the aquarium owners that experience this poisoning had not chosen to buy that sort of coral,” Dell’Aversano said. “Sometimes it came as a hitchhiker with the living rocks.”

Four years after finding toxic Palythoa in Washington, Deeds and scientists with the Centers for Disease Control and Prevention released another report, this one detailing 10 cases in Alaska. In an interview, an aquarium shop owner told the researchers he suffered the occasional bout of flulike symptoms — possible signs of poisoning — but didn't think much of it.

There is a lack of laboratory data about the toxin's potency, Deeds said. “With this limited information, it is difficult to make recommendations on potential hazards.” What's more, the FDA, Deeds's agency, does not regulate pet coral. It cares deeply about what you ingest, which is why Deeds's lab is equipped to test for palytoxin contamination, but very little about what you keep in a tank.

Dell’Aversano and Tubaro recommended wearing gloves when handling coral, and avoiding brushing coral or exposing it to hot water. A recent lab study, authored by the scientists, revealed that filtering water with activated carbon or charcoal neutralizes more than 99 percent of the chemical.

Cutting-edge hobbyists — who must understand water chemistry and marine biology — work in concert with scientists. Growing coral reefs indoors “has a tremendous conservation value,” Rhyne said. These reefs won't ever be the basement equivalent of a doomsday seed vault. But, as reefers develop new techniques to raise coral, scientists benefit, too.

“Scientists generally all use the hobbyist equipment,” Rhyne said. Several coral researchers have applied reefer methods to their laboratory studies and conservation efforts. A public aquarium in the Netherlands now breeds coral, a feat not possible without the aquarists. “They can condition the coral to spawn on cue,” the biologist said. “That’s all from the hobby.”