Did you do a water test to verify the probe is accurate? Probes are notorious for this.
Fwiw , ph in your tank falls into place rather quickly for the new salt to raise your ph would be a temporary number while c02 went to work , the water change would have to be huge to change the whole systems ph value for 12 hrs , usually it goes back to average levels within a few hours.
Fwiw ...they don't add ph to a bucket...well they do but it's in the forum of alkalinity as the two are linked ( reson why its affected by c02) so test the Alk if it's through the roof you have your cause , if it's normal range then I would be looking at the testing device.
Hcl I would not be adding to a running tank , it's very aggressive and if your ph probe was out then you'll cause more harm then good .
__________________
........
|