I'm figuring 27,000 gallons to be safe on the low end. From the math that I've done, the pool should be 32,000 gallons. However, when I add chemicals, they seem to have a "larger" effect than expected so I did some calculations based on the last batch of bleach that I added to the pool and it calculated out to 27,000 gallons. I added 364oz of bleach and overnight my FC when from 1.5ppm to 8ppm. I plan to do the same calculations on the borax addition to see if the effect is equivalent to 27,000 gallons as well. By the way, how do you test for borates?