I have an Aquasana water filtration and conditioning system, where the treated water is fed into my hot water tank. I got the system because I live in south Florida and notices the water was green when you filled a bath tub, which I didn’t like.
I also selected Aquasana because it does NOT soften water, but it does “knock the arm and legs of minerals off the water molecules” in its conditioning tank. They told me that this keeps the hard minerals in the water (so no “soft water” feeling when you shower, which I don’t like), but they said it would keep the minerals from messing up pipes and plumbing the way unconditioned hard water does. I know you have noted that “soft water” makes the “rotten egg smell” more likely and I’m wondering if this different method of dealing with the hard minerals also makes the “rotten egg smell” more likely.
Also, you have a kit you sell for easily killing the anaerobic bacteria inside the hot water tank water with peroxide, which I am thinking about purchasing (because we do go away for weeks or months at a time and we have noticed the “rotten egg smell” upon our return and it can’t just be flushed out by running the hot water tank empty. Do I need to replace the anode rod (even if recently replaced already) any time I come back and introduce the peroxide to clean the tank water?
The H2S (Hydrogen Sulfide) (naturally occurring) in the water is the cause of the odor. The WH temperature enhances the smell. The use of a salt-based softener changes the pH of the water making it more acidic and aggressive on the WH tank, hence the quicker breakdown of the sacrificial anode rod (better than the tank liner itself).
There are specialty treatment systems available ($$$) but in your situation (long absences) will not help the situation. All you need is the kit offered here and use the peroxide once a month (while there) and when you are going to leave for awhile and upon return.
Make sure you flush the WH on a regular basis as sediment(s) are a food source for bacteria.
BTW– The hydrogen peroxide you buy in the drug store is not food grade.