Hmm...
This is where I feel a little bad. I disagree with a very respected member. Not in the technical details as they are absolutely correct. More at how we view the big picture zoomed all the way out to the total end result level.
Acids All The Way.
If it is true that we can take the carpet up to a pH of 12.5 and between the forces of soil, extraction and rinsing with alkaline solution at very dilute quantities and get back to 9, then rinse with an acid rinse and get back to 7, then skip the middle man.
The reality is the carpets that have a positive charge (acidic) resist soiling better than carpets with a more negative charge (including neutral). Alkalinity and acidity is a continuum. Why not effect not just a near neutralisation when you can achieve a wholesale reversal.
Its rare where it's possible to do something so ideal for the carpet. I think it's accepting a passible compromise to finish jobs with an alkaline rinse. Good acid rinses have neutral water softeners and surfactants to serve as rinse aids. Water is naturally inclined toward becoming acidic as it's temperature rises. Add some other acid solution to some water and make some liquor, then heat it, you get a further bump in acidity that's only temporary and residue free.
@Mikey P has nailed it. Use acids all the time. Leave alkalis to restaurants and grease pits. And even these clean up well done right.
If you are resorting to spiking the pH of your solution you haven't preconditioned adequately. Go back to WATCH, what can you do to make it balance out and get your result - before - the finishing step.
Carpet fibres are a "domain" to water molecules. They occupy it. Whatever goes in first will be the last thing to come out. Thats a FILO system. First In Last Out. Whats the first water based liquid you introduce to the domain? Your soapy as shit pre-spray.
Think about that.
Who starts their extraction with a "dry" pass. We all should. We should all try to suck up that soapy stuff without putting in any more water. More water simply dilutes it but also drives it an and ensures it's now harder to get our "first" in chemical back; we know that is the "last" moisture to come out.