Prices for an additive used to clean fish tanks have skyrocketed after studies found the pharmaceutical drug version of it may treat the coronavirus, a report said.

Chloroquine phosphate is used to in aquariums to kill some organisms, like algae, that may harm fish.

Sellers on eBay and other websites hiked prices in March, and buyers were willing to shell out large amounts of cash for the substance, Storyful found. The listings indicated that the product wasn’t meant for human consumption.

Between Feb. 25 and March 2, the price paid for a single 25-gram bottle of chloroquine phosphate rose from $9.99 to over $500.

On March 18, eBay’s tracking indicated that one seller had sold 84 lots of the substance in 24 hours. By that afternoon, all sizes were sold out save for 100 gram lots, which were being listed for $519 each.

The anti-malarial drug chloroquine, and a derivative of it called hydroxychloroquine, have been found effective in killing the virus in laboratory experiments, according to some recent studies.

But the drug hasn’t yet been approved in treating COVID-19.

President Trump on Thursday said the drug would soon begin to be distributed to treat some coronavirus patients. FDA Commissioner Stephen Hahn clarified that the drug would be made available as part of a clinical trial.

“That’s a drug that the president has directed us to take a closer look at as to whether an expanded use approach to that could be done to actually see if that benefits patients,” Hahn said. “We want to do that in the setting of a clinical trial.”