There are life-forms that thrive in scalding water. All it takes is enough minerals. Visit Yellowstone Park and you're going to smell a lot more than sulfur.
It takes something more than a clean water flush to eradicate the life forms.
If you can find a way to introduce 10% concentrated vinegar, set the hot water heater on high and let the vinegar set for a couple of days. Drain but not flush the heater..,
Then pre-mix a full pound of baking soda and put that into the heater for another couple of heated days...
It will not only sanitize the heater but when you flush the heater expect to see a pound or two of minerals come with it.
Useless mineral removal wise to do this flush without baking soda neutralization as the soda is what does the trick -- after the vinegar.
Have a humidified CPAP or BiPAP? Is the aluminum disc coated with ugly minerals? Heat a 50/50 mix of vinegar and water to boiling. Fill the chamber and it sit on the counter.
WITHOUT DRAINING IT
Add three tablespoons of baking soda and mix by shaking.
Whoa! Looks like new. Rinse.
Strange diseases and afflictions are derived from bacteria growth.
With the humidifier chamber, hose and mask weird respiratory stuff like Legionaire's Disease isn't so funny. Change hose sanitize mask.
Until I cleaned out a year-old water heater down here I kept getting eye infections. Somehow simply sanitizing the water tank missed it. After vinegar and baking soda my eyes cleared up and stayed healthy.
You got me. I just live here..