Wow - lots of posts here.
Next time you have a pH reading of 8.0, just toss in four dry ounces of dry acid.
Get a measuring cup next time you go to the dealer, or run over to Wally World and get one.
Most tub makers and chem companies don't suggest adding more than three or four ounces at a time - so you may have to repeat this. Wait at least three hours for the pH to settle at it's new level.
For my 500 gallon tub (now gone from my life
) I have to add four to six ounces on fresh water to even start to get it into range.