Wow that's great info, its good to have a stepped method that one can build on and improve. before I was just guessing and never seemed to get the results I wanted and now I know why. I did test the bag water for toxins which only had 10 PPM Nitrate.
Ill take what you said into consideration but most importantly will take additional precautions with my new Blood Parrots using a QT tank, heater and even pre-matching the QT tank water to the bag water in both PH, GH, and TDS using this water to drip acclimate for a few hours before adding them to the QT and then to the tank after an additional 24 hours PH acclimation to my standard 8.2 PH water.
I don't know what these local LFS are doing to maintain 6.5 to 7.2 PH as they say they only use tap, but it is well known that the entire town is a water softener town due to the high PH and 600 PPM GH well water off these mountains.
As far as lfs water is concerned, I am sure they are on central system.
I dont think they are hiding any water treatment equipments since such can bring in more sales.
Only thing I can see is that their system(s) have been running for long time. As you probably know, their system hold lot more fish than most hobbyist tank thus by having more fish, pH are bound to drop with time. They may had waited until ph dopped to low and Perhaps they have figured out the amt and frequency of water changes to maintain stable pH of system within range you mentioned, provided that they are using same water from same resource.
I dont know if this method is possible but have yu ever considered Rain Water.
why dont you collect some in inert container and run some test. If rain water is close to or even acid water, perferct water to be used during pwc.
What I've done with rain water was to run filter with high quality carbon and heater before using. Even ran UV sterilzer, Ozonizer to see if I can improve water condition. But found not necessary to use high-tech Eq.
I even baked those used carbon in broiler chamber when Mom was using oven. No need to waste energy when I dont have to. lol!.
Trying various alternatives to save or should I say not to waste any! Even to a point recirculating dirty water from tank via diy water treament contraptions. Hey it worked and will work when properly maintain as long as one build good ventilation within such system room (I calle it Mech Room)
Ive been following your original posting on other forum (I am barred from that forum, lol) and I was intrigued by all the attempts and trial/errors performed by you since it reminded me of me some 40 yrs ago and still continuing. LOL
Good Luck with all the experiments and lmk if you opt for alternatives plus your results so other can utilized such info provided they keep their mind open.