We have a hot tub, I built it before I finished the house. For us the tub is a necessity not luxury. We are in the tub, the whole family, every evening. We are professional skiers, the tub is a must after coming home from the mountain.
I've never found anything other them the chems you mentioned, we use what is nessary. We do have the smallest heater [it would take many hours to heat the tub from cold to hot] the tub comes on every so often burns very little fuel and is at temp at all times[ like a tankless
water heater] rather than a big furnas with lots of BTUs, less fuel that way.
If we had Natural Gas, instead of propane, at valley ranch 2 we would have one there also. We have a cool tub there that is not heated, we use it during summer diving in to cool off, we don't use AC, we do have a swamp cooler that we use if guests come in summer. There,at 2,we heat with
wood to use less propane.