All sedimentary limestone and aragonite contains phosphate of varying levels. It’s been known for decades, before BRS ‘discovered’ that dissolving that rock in an acidic reactor releases it back into solution.
Further, phosphate in aquarium water, or oceans, will spontaneously precipitate on calcium carbonates, increasingly with pH.
fwiw,
I’ve written previously about washing rock in citric acid solution to help mitigate this issue.