Grocery store baking soda is what we all use. Start with 2 cups worth and
recheck after 24. hours, depending on circulation YMMV. I'd liked to know
what your pH is? Baking soda has a set point of 8.4, some say it will bring
down a pH higher than this.

If anyone out there has experience with bringing down a pH with baking
soda, I'd like to know just how much does one needs to add? I've used up to
2 pounds in 1,000 gallons and didn't see the 9+ pH budge. Testor goes to
9.5 so I had the range to know just how high it was. ~ jan

OK, so I got a pond kit to test my bond.
I read it as the ph level was too high and the total buffering
capacity was too low. According to the instructions I have to add
Sodium Bicarbonate (baking soda) to bring it up.

My question is, is the standard baking soda in the grocery store ok to
use as long as I just get pure baking soda? If so how much should I
add?
My pond is about 2000 gallons.

Thanks for the info.

(Do you know where your water quality is?)