Your total alkalinity drop won't be instantaneous. It will go down gradually. Stop measuring total alkalinity so often... just worry about pH/FC/CC for now. pH and total alkalinity are related. If your pH is wacky... your total alkalinity is probably wacky. If pH is fine... then TA is probably fine. Makes sense? So just measure pH regularly for now and leave total alkalinity, calcium hardness, and CYA for monthly testing. Only pH and FC/CC are routine things.
I would not lower pH. Just leave it at 7.4 and check daily. When it gets to 8, lower it to 7.2ish and repeat. Your total alkalinity will gradually work its way down and you will notice your pH will stop fluctuating so much.