Cusser

No. Water boils at 212F, ALL the water would've had to be evaporated for that to happen, and typically there's a flow witch to interrupt voltage to the heater.

You could temporarily try a rubber stopper in that hole, and then see what happens. Ace Hardware sells individual stoppers of various sizes, in the small drawers, inexpensive.

My pool ladder is 21 years old, in the Arizona desert. The steps swing up for child protection if one needs that.

Soaking in vinegar or vinegar-soaked rag can remove water deposits. I wouldn't use any "sealer" on the threads, the seal is made by the gasket. A little RTV or Permatex Aviation on the gasket surfaces might help.

I would say to stay current, just limit your time. Mrs. Cusser is an addict for online so-called "reality" shows, spends way too much time remembering (and unfortunately trying to tell me about) those people's lives. Why should I care who marries life-imprisoned convicts or that Teen Moms now make their living from the show and live in nicer homes than I do?????

I believe that Canadian Spa Tech means that a pressure switch or flow switch will NOT activate, so no power will be delivered to the heating element.

Got my cover holder like 20 years ago; it's two metal bars, bent like in photo.

Elbow grease and a green scrub pad. No soap or detergent, will then foam almost forever !!!

If the housing is not cracked, I would think a new O-ring or new gasket might fix the leak. If a gasket, and not available, I might try a thin film of RTV on each side of the existing gasket, or cut a new gasket from rubberized sheet gasket from the auto parts store.

Is it leaking from the hose/hose clamp, or from the body of the assembly?

Given my experience with a similar-size spa, I'd say 5 minutes with jets on should provide plenty of mixing. I don't use test strips myself.

Not on my 1988 CalSpa, just need to get the water level over the drain. If I need to, I can plug the skimmer hole with a big rubber stopper.

Yes. My old spa is about 350 gallons, and no big deal to drain and refill; if I'm there during this, I use the under-$100 immersible pump I use for my above-ground pool. Biggest "work" for me is manually bailing out the last two inches of water, and then cleaning (rubbing) the sides/surface by hand. When filling, I usually add fresh water some, then drain again, maybe even repeat, to get as much of the "old" water out of the plumbing.

When one drains a hot tub, cannot get ALL the water out, some residual stays in the plumbing. As a chemist in the soap and detergent industry, it takes very little surfactant (surface active agent such as soap from fats from bathers' skin or detergent) to make foam like that. I'd try a little silicone anti-foam.

I've had my CalSpa since 1988, and have used sodium carbonate to raise its pH, and have never used any borates of any kind. I've also used sodium borate for similar in my above-ground pool. On a few occasions I've used powerful 100% sodium hydroxide powder to raise pH in the CalSpa and in my 15' above-ground pool, but this is significantly more dangerous to add (wear gloves, goggles). https://www.acehardware.com/departments/plumbing/drain-openers/drain-cleaners/4239216