Doesn't sound like you're gonna need the baking soda anytime soon!! Just wanted to make sure that you're using Borax instead of washing soda, which would bring the TA back up and defeat the purpose of the muriatic. The boxes are next to each other at my grocery store, and look similar except that they are different colors. Only thing I know to do is to add more muriatic and repeat your ratcheting process until you get it where you want it. Just make sure that you keep a close eye on your pH--you don't want it to get below 7.0 or you risk damaging your liner. Make sure you raise it up enough between acid additions so that after the addition, it's still 7.0 or higher. Is your fill water high in TA? That may be one reason why it's so high and is coming back up if you're having to refill frequently.

Sorry I don't have a more concrete answer for you, but sometimes we just have to "treat the symptoms", even when we don't understand the cause!!

Janet