Got a call this am from one of the Contractors I occasionally work with, he’s in a pickle.
They poured concrete back in December 2023, a few days later it rained and got stained… Coustomer had them come back and clean it, my contractor had them wash it with Muriatic acid (not sure why) and once it dried it yellowed.
My guess is, the acid wasn’t neutralized and it reacted some how.