I think people would pay for the "hands-on" education to get started. It somewhat feels like you're trying to get a drink of water from a fire hydrant when you're first learning your way around.
Charge ($50?) for the initial consult. You go to the pool and have a look, use your own kit to test. Tell them you specialize in providing the education of the TFP method and hand-holding while they learn it, but if they want to merely receive daily instructions on what to do for the remainder of their pool days, you're fine with that too.
You can have each client purchase their own kit, instructing them to the TFP site, along with specific directions to buy X gallons of X bleach from a specific store, and whatever else they'll likely have immediate need for according to the condition of their pool. Also check out their tools and specifically tell them to buy X from X store.
If they don't want to mess with the gathering of all the items, you can provide that service for them also for a charge of ($50?) plus the cost of the supplies.
Once they (or you) gather all their loot, they make an appointment for you to come and show them what and how to test.
Daily, (for a charge of $7/day?) they email you the test results, pics of the water, and a description of the water. You respond via email and tell them specifically what to add and do.
After a week or two of this (whatever they are comfortable with), you start with the true educational part - telling them WHY they're adding this or that, etc. You do everything just as specific as before, but you also provide them with the specific text from TFP that's relevant, along with a link so that if they are so inclined, they can read it from the horse's mouth.
They may do this for the rest of their lives. That's fine with you! But if they "get it" prior to having paid you ($500?) and no longer need you, they pay the balance of the $500. And they're always welcome to email you in the future for advice at a rate of ($10 per day?) if something goes haywire.
You could also offer additional in-person visits just in case something goes amiss and you need to see things in-person. ($25 or $50?, maybe depending on where they are in the contract or depending upon circumstances).
As for how they would pay you, it would be via check in the mail once per week, weekly via PayPal (adding in cost for what PayPal will charge you) or via a direct transfer from their bank to your account (some banks even do transfers via cell phone numbers).
Easy peezy!
(And for this business plan, I'll only charge you a visit to my pool to teach my pool guy the TFP way. Lol!)