Hi TooCLool,
if your CYA is 100 or above, the only rememdy is to drain and refill however much necessary in order to the the CYA down. Just be thankful you are not in California!!
TA of 70 might be just fine. What TA does is buffer the pH. If pH is very unstable and you have to add muriatic acid or pH down often,, you want TA be on the low side...so 70 might be just fine. No way to know however until you can measure it often and lean what the pH is doing.
I would recommend not to add anything until you can get a good test kit.
And you are right. The pool stores REALLY want to sell you stuff. That is their 1st priority. Thats how they make their living. What it does to your pool is relatively inconsequential. If it messes it up, you'll just go back to buy something else. Thats what they do.
All you will find here at TFP, is a recommendation to be able to accurately test your own water with a good test kit, and then add only what it needs. No one here wants to sell you anything.
Once you get your kit, and you decide to maintain your pool the TFP way, you will be flat out SHOCKED *pun intended*, at how easy and inexpensive it actually is to have absolutely clear, clean and sparkly pool.