Folks,

We've gotten off track. His original question asked if 3lbs of stabilizer would have a dramatic affect on his pH (8.2 down to 6.8).

stabilizer will cause a lowering of the pH. It is cyanuric acid with the operative word being acid. Just make adjustments slowly with borax to bring it up.
The above statement is simply incorrect....given the intent that the questioner asks, 'could his CYA and the 64 oz of muriatic he added have affected his pH that much?' There is no chance That adding 3 lbs of CYA to a pool will DRAMATICALLY decrease the pH. If that were true, imagine what the pH would've done if he had tried to raise it by 40ppm!!

using Michaels calculator, it looks like a 26k pool needs 1.15 gallons of muriatic to lower the pH by 1.4.

How was the testing conducted? Have you tried the same test again? I think the accuracy of one or both of the tests might be an issue.

Mad, run your tests again and be really sure your pH is where you think it is. Raise and or lower it with Borax and Muriatic Acid. Use Michaels calculator to figure your quantities. The affect CYA will have on your pH will be FAR less dramatic than implied above.

Dave S.