Welcome to the forum! While there are many more people with great chemical expertise than me, I do offer a little advice. We had a rule called, "Chas' law (from a now retired member who frequented here) A month after you get the tub, dump the water and start over, everyone screws it up at first.
We use our tub mainly late in the evening, I'll check the sanitizer level in the morning. But when it comes to PH, I do offer this one piece of advice, after adding something to make the PH go up for down, wait 48 hours to test it again to give your adjustment dosage time to settle down. A lot of people say wait 24 hours, but I wait 48 to avoid chasing the PH up and down.