PH floating to high

I have just put together an aeroponics system using the fence posts and net pots.
I am using Hydroton medium.
Anyway I started it up last night with a few plants (10) that are two weeks old using 1/4 strength Dutchmaster gold.
I live in the country and am using tap water which has the hardness of around 320 (alot of calcium).
I adjusted the PH to 6.5 at start up (using the vial and green dye) and this morning when I checked it again it was a HARD 8.
I adjusted it and came back 2 hours later and it was way up again.
I have adjusted it three times since.
I used to do this indoor grow thing along time ago and remember having to adjust it maybe daily not hourly WTF am I missing?

Did you let your water rest for a day or 2 before mixing? This is what I do to let the chlorine evaporate.
Also did ya wash that hydrotron well before using?

sounds like your tap water is horrible. just let water sit out for a day or 2, pour all the water out and clean the tub with peroxide, then refill with cured water with nutrients.