Hello newbie, and welcome to TFP!
We'll help. First, whenever you need to lower TA, you can do so with muriatic acid. You can use dry acid, but of course you have to mix it, and it's just a bit of a pain. It may also cost you a l ittle more, especially at Leslie's. You can get muriatic acid at many local hardware stores (or Lesiles too). To lower TA, the acid lowers TA AND pH, so the trick is to watch the pH at the same time. If the pH gets too low while you are lowering TA, use aeration to naturally raise the pH as noted here
Pool School - Lower Total Alkalinity. Oh, and yes, whenever adding chemicals, the pump should be running for at least 30 minutes to adequately mix everything. FYI - Here is a list of TFP chemicals:
Pool School - Recommended Pool Chemicals.
Now that your pool guy has left, do you have the right test kit? You MUST have one, and the pool store tests don't cut it. Please see the TF-100 link below I my sig to ensure you have total control of your water with accurate results. It should be priority #1.
Also, please add your pool info to your signature by going to the top of the TFP web page (just under the Pool School button) and select "SETTINGS". On the next page look to the left for a menu bar that says, “MY SETTINGS” and go to "EDIT SIGNATURE" to enter your pool and equipment info there. It will help us later. Nice to have you with us!