We use a product called HtwoO and it's widely available
Whilst they want pet friendly they won't strictly get the results in doing so. I'd use non caustic tfr with wax, rub up, rinse off and then DDAC . The other option is just lob the DDAC on out of hours and wait for the result
I'd swerve the black wash as you need to deal with fumes as well as run off. Why do you buy blackwash rather than neat SH
Could you wet vac up any residue?