PP makes a good point.

And while I don't think Chloramine is the culprit it does seem that water is the key here.
I'd just buy a couple large dustbins, line 'em with plastic, chop into a downspout, and wait for rain.
Even highly acidic rainwater beats groundwater north of PH8.

It no rain there?
Electric distillers are available, but costly to feed.
If you have roof space, I'd suggest a solar still for low rainfall areas.
They are easy to build. Google it.

As I stated, Chloramine is not the bad guy here.
It can kill fish, but it actually seems beneficial to my plants. (kills waterborne pathogens)
However, that's assuming that your water supplier knows how to use it properly.
From your readings, they do not!
That, or it's time for a new meter.

Chloramine can be removed from your water if you wish.
Just buy some ascorbic acid, (vitamin C.), and use it as your PH down.
It breaks Chloramine down without harming tropical fish.

(Or, you could go to a pet store and pay 30-40X as much for the same thing with a different name.
That's what I used to do until I read the bloody label. )

At the least, I'd buy enough bottled water to confirm my diagnosis before proceeding to costlier remedies, yah?

It, only takes a minute to pop one out of the pot and look at the rootball.
Suggest that you do that, and if you see areas with a white, waxy looking substance, get back to me,.
That might be the actual culprit, root aphids!

Aloha,
Good luck
Weeze