@Byron: I called them and they sent me to a website I hadn't been able to find when I looked before. We've had trouble here in Salem with cyanotoxins from algae in the water and they adjusted their filtering because of it. They add powdered activated carbon and keep it suspended in the water, and the cyanotoxins attach to it, and then it goes through a 'roughing filter' of a layer of sand. Then they add some acetic acid (vinegar) and it goes through slow sand filters. Then they add chlorine, fluoride, and (you expected it, I didn't) soda ash. They are working on an ozone cyanotoxin removal system that will be done in spring 2021. I was promised I'd get a call back tomorrow and was planning to ask what the pH is of the water before they add the soda ash. Would there be anything else I should ask?
I cannot comment on some of those additives, but the soda ash is what I expected as it is common with low pH water. It is temporary, which is why I can do massive water changes and the pH only rises a decimal point or two. So again on the pH, leave it alone, it will lower and stay there at whatever level it stabilizes at with reference to the organics. If they can tell you the natural reservoir pH before they filter/additives, fine, just for the record, but the biology of the aquarium will have more effect on pH in the end.