Swapping to BBB but what about CalHypo

[Watermom]

Calcium level between 200-400 is what you should aim for.

Is your volume 1100 or 11,000 gallons. I think the 1100 is probably a typo in your post above. If it is 11,000, I'd start with a half a box of Borax. Give it a couple of hours to circulate, then retest and redose as needed.

[RobDHW]

Yes, Watermom - I can't type. 11,000 gal (although, I want to recalculate... today is pool maint. day).
I went to poolcalculator.com and figured out that I'm going to add 4lb baking soda, since my TA can be raised a bit, then I'll add some Borax. Test again. repeat.
I also need to add serious calcium per the calculator. I bought some, which I will add, then once again test. Repeat as necessarry (or however it's spelled).

I'm so happy that I found this site, from the bottom of my wallet and the top of my brain.

[Watermom]

Do the Borax first. Low pH is a much bigger problem than low alk. And, actually, TA of 70 isn't bad.