If your pH was below 7, the starting TA was probably not 80. For a pH below 7, a TA of 30 makes more sense.
Most likely, you had testing errors before or after adding the pH increaser.
What is the history of the chemistry?
If your pH got below 7, it implies that you let the chemistry get away from you by not monitoring it enough.
Sounds like a lot of tab use with insufficient testing.