It looks more like mould to me which is irreversible
formula 90 powder is a highly buffered cleaning detetgent, I use it all yhe time, Ultimate master has its uses but was originally designed for wool carpets, it used to have the woolsafe logo on the tub, but as they tweeked the chemical over the years they had to loose the logo or pay an absorbamant amount to have it re tested
Its also not a buffered chemical so it soon loses its ph when sprayed onto the carpet
stuart