Hot tubs are very fun, a huge quality of life improvement, and also much more expensive than you might think at first blush. If you're like me, you searched "hot tub" on craigslist and thought, man, there are a lot of free hot tubs in this world! Or maybe the first place you searched was a hot tub store and thought "$5000 for the cheapest, yeah, nah." Even a free hot tub isn't cheap.
Luckily for the cheapskate, the world of plastics has just absolutely EVERYTHING to offer these days, including durable, enjoyable, affordable hot tubs!
SmartSoak is an extended review of and indeed improvement upon just such a product, taking things two or three steps too far at each turn.
Check out the project logs for all the details. You probably want to read them start to finish, so scroll down to "Log 1" first.
Github repo with node-red flow, though no documentation to reproduce: https://github.com/alexwhittemore/HotTubPi