Wish me luck.

Borax only effects pH. What tester are you using to get the 4 ph you reported?

Same stuff --
 

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OK -- the OTO you did with the pH looked pretty yellow. No need to do that chlorine test, always do the FAS-DPD.

Use pH of 6.8 in all Poolmath calculations. Never guess extrapolate.

Using Washing soda, add 12 oz, circulate, and test pH. continue that until you see the color of the pH test in the range of the tester.
 
You need to figure out why the pH and TA crashed. It is very harmful to the liner in your pool.
 

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