Unfortunately, the 2 big reasons you bought your tub- hot water and the bubbles- are going to keep your water balance in constant flux. The hotter the water is, the more the pH wants to rise on it's own. Also, every time air is induced into the water, either by your tub turning on to cycle or by you turning on the jets, the total alkalinity will slowly drop.
Try testing your water and balancing once a week on the same day for a few weeks in a row, and you'll notice a pretty regular pattern. One of my employees, a high school student, did this with his own family's tub, and found that based on an average week, he could make a very good calculated estimate of how much TA increaser and pH decreaser he needed to keep his tub maintained.
Also, your pH may be starting high if you're using well water, which tends to start with a high TA and pH.
One last tip, ALWAYS adjust the TA first, wait an hour or so, and then adjust the pH. You will likely waste time and chems with little result if you do it the other way around.