Thanks for all the replies! You have been insightful enough to ask about what I forgot to consider to provide and also some good possibilities.
The plumbing does not leak at the moment. I will come back to that with the hot water heater.
The environment around the hot water heater tank is extremely dry in winter (up to 35% relative humidity when drying out ski clothing; not great to put in an electronics lab) to quite damp in the summer (up to 80% RH). The well water is quite cold due to the well depth, so condensation is an issue in summer. There is a length of 1 inch copper pipe stored in the same room and remains at ambient temperature which appears in excellent shape. That would likely rule out gas in the air. Under the kitchen sink is upstairs and should get a reasonable amount of ventilation and stable temperature/humidity. However, under the sink comes along with storage of plenty of cleaning chemicals.
Would calcium sulfate be an indication that the water softener may not be operating properly? My understanding was that should replace all calcium with sodium. Testing for ions sounds like something worthy to follow up on. Does that testing differentiate between different types of ions, since I assume there will be high levels of sodium ions? That could lead to the suggestion of the ion exchange column.
pH was measured at a tap, so would be the same water as in the house supply part of the system.
@Red Squirrel, since you are also in Canada, can you recommend a suitable clamp meter or specs? I would assume any currents would be relatively small and a cheap meter would not be helpful. I can always use more TE, so long as someone else does not consider it blowing the budget.
It sounds like investigating where that grounding cable goes could be useful as well.
Currently, the cascaded filters are 2 stages including charcoal down to 5 micron. What would be the benefit of 0.3 micron? My understanding is this size was to filter out bacteria and larger viruses. The filters are after the pressure bladder, rather than the suggestion to put them before. I was recommended to have the final stage after the water softener.
Any changes to the piping that I am doing as I go use PEX. That results in fewer joints. However, the joints in PEX are still an issue, as seen in the supply to the hot water tank. I have some nylon fittings to try out to see if that is any better than the brass fittings to connect PEX.
Whole house reverse osmosis is not going to be economically viable. I calculated that buying the large bottles of drinking water would still be less expensive than a reverse osmosis system for only drinking water over at least a 50 year period.
The hot water heater was replaced 5 years ago. The old hot water output nipple had corroded off, causing hot water to spew all over. I caught it quickly
and had the tank replaced. The new tank started to have a small leak in the pressure relief valve after 4 years and I replaced the valve. Replacing that valve was just enough to crack the hot water output nipple as it was heavily corroded similar to the old tank, but this time was able to re-tap the thread. Oops, it is not shown in the photo, but the hot water output looks okay after a year now.
The new tank has been flushed but not fully drained from the drain faucet yearly; only a bit of red material was noted initially and then the water would run clear; probably the same rust as suggested elsewhere in the system.
One interesting thing to note is that I also flushed from the pressure relief valve at the top of the tank also. I observed a small amount of gas would release before a bit of red-colored water and after the water would run clear.
The sacrificial anode is something I have forgotten completely about. It has never been checked or replaced. How long is the anode when new? I have limited clearance and may not be able to easily remove or install it. I understood the anode protected the tank, but I get the sense from your responses that it may be meant to protect the whole system?
Note to myself: any future work should consider at least a somewhat easy way to disconnect the tank and tip over for access to the anode if needed.
Now I have some leads to follow up on...