No chemicals, no electricity, refill and clean after each stay, and “environmental friendly”.

It also seems to be more common in some areas of the country more than others (due to much older construction in the region, higher exposure to harsher climates, older electrical and plumbing running through the home, etc.).

We do not drain our hot tub after every guest, but we do test and adjust the chemicals, vacuum it (sand) and skim the top if needed after every guest. 

If I were you, I'd go for the heat treatment as long as it's immediate and kills eggs too, because chemicals need to be reapplied. 

I have learned to get a cheap maintenance person and have them buy the good chemicals from A1 Able and spray it for you.

I used to work for a start up, we sold maintenance software to big oil and gas, chemical companies and other big producers.

That includes weekly cleaning, chemicals, flushing of filter when it needs it, topping off the pool, and my people clean the pool deck when it needs it.

Look at the topography and terrain to determine how.Evaluate fundamental infrastructure and service availability, as well as expose examples like wetlands and flood zones, protected lands, hazardous chemicals etc.

Everything I read online says DO NOT use exterior stain on the interior due to the fact it gives off harmful chemicals. 

Gets bad by July, Aug ish, and Sep we see harsher pivot.