What humor?
Zing! I gotta million of 'em.
Let him and Leslie's take care of the pool then, 100%. Offer to do it, your way, no intervention from him, or offer to let him do it his way, no intervention from you.
Or a long-term project. He likes accounting? Start a ledger, include images. Track how much it costs running a Leslie's pool with hubbie at the helm for one year. Or what it costs if he goes back to the pool guy. You may or may not want to swim in it. If he makes it a year, then you get your turn (and get to drain the mess he's made, on his ledger, include that expense). It's just as likely the pool will be trashed in short order, before his year is up. Perhaps a ground rule is: first one that lets it get green has to pass the baton to the other. When you get your turn, and a fresh fill, that'll be the end of the debate, and you won't have to refill the pool again at the end of your year. Your TFP pool will be clear and clean and look and smell and feel fantastic, at a fraction of the cost of any other method or service he may have tried. He won't ask for the task back...
If it's any consolation, I've yet to convince a family member or neighbor or friend to convert. In fairness to your husband, his resistance is not uncommon. TFP methods are, at first glance and without understanding the science, almost too good to be true. No pool guy? No pool store? A fraction of the cost? Better, healthier water? When people have been using pool guys and Leslie's for decades? It can be a tough sell, and sometimes it takes a completely failed pool to get them to try something else.
One unfortunate caveat to my advice... Mismanaging pool water is one of the primary reasons for premature failure of a pool's surface, including the kind you have. Mine (just like yours) lasted only six years because of pool guy methods. It cost $9000 to make that right. Your husband's stubborn resistance will result in unnecessary out-of-pocket expenses, and quite possibly very high expenses. And will possibly (probably) cause some amount of permanent damage. Hopefully the damage will be negligible. I hope his stint doesn't cost you too much before he can be "led to the light."
Good luck.