Robin, have you seen this product.....Chemspec One Earth Carpet Cleaner & Prespray Powder from Restormate?
Robin, pardon my ignorance but you say to use at full strength 12.5ml/litre, if this is a powder how would you measure it? does it come with a measuring scoop in the tub? I have a 8L pressure sprayer so usually make up around 5L of pre-spray at a time