The reason the TA went to 80 is a bit technical but in a nutshell you have shifted some of the carbonates/bicarbonates that make up the TA to carbonic acid which the TA test doesn't measure. As long as the carbonic acid is still dissolved in the water it will reconvert to carbonates/bicarbonates if the pH rises. If it is driven off by airation then the TA has been lowered. What is your calcium hardness? TA of 80 is certainly within range if the CH is in proper range.