Well, with that nasty tap, you better buy RO, not for the plants, but for you!
What on earth are they doing putting all that NH4 and PO4 in the tap?

I'd be pissed off. I have a water treatment operators' license though.......
Well, this is good news as far confirmation.

So dosing with the tap (please, use the RO for drinking and cooking , washing etc is fine, never give such foul water to kids/infants!):

K2SO4
GH booster(mostly K2SO4)
Dose about 1/2 the KNO3 after water change, then normal on the 3rd and 5th day after the water change.
Traces etc.

That's some nasty tap water.

Regards,
Tom Barr