very high ph water need help

hi everybody, i have been experiencing very slow growth so i did some ph tests and i discovered that the tap water i have been using has a ph of 8.5 to 9 so i decided to transplant my plants into a fresh soilless medium ph of 6.5. I started using hydrochloric acid to adjust water ph to 6.5 before waterings. now i have noticed after only two waterings in the new soil that the soil ph has risen again and is about 8, i checked my water and the ph is rising back up to 9 after only three days? is the ph of the water rising in the medium before it gets a chance to evaporate?? Should i be using something other than hydrochloric acid?? Whats the best product to use lower ph levels in water and keep them low? I was also thinking of adding some iron sulphate to the pots to lower ph back to 6.5? Thanks heaps for any replies this is really frustrating me and any help would be great. thanks in advance dave.

Use ph down from a grow store, what kind of meter are you using? I seriously doubt ph raises from 6.5 to 8 in a matter of days, , what kind of soiless medium?

im using universal indicator and checking the run off from the pot. My soilless mix is 50:50 peat moss, perilite.

Enlighten me on what a universal indicator is? If its not digital your reading is off...

Also if your taking a reading before you put the mix in the pot and take a reading of the "runoff" of course its different, I was am never a believer of runoff readings I think they're a bogus way of reading your plants ph.. my opinion

you put a drop in the water and the indicator changes to a colour that indicates the ph of the water or solution eg acids yellow to red alkaline dark green to purple neutral green