In Pool Math, I put in 20k gal pool, TA=100. In effects of adding chemicals section, I put in 128 oz of dry Acid. The result is pH lowers by 1.07. This seems too small compared to real life. Is the calculation wrong?
It is an approximation and can be fairly far off sometimes. The effects of adding chemicals section uses a rather approximate method to calculate PH changes. The PH section uses a much better approach and is usually within +-10%. But the effects of adding chemicals section can sometimes be off by far more.
The calculation is actually dropping too much. In a 20,000 gallon pool with a TA of 100 ppm, adding 128 ounces weight of dry acid would lower the pH from 7.5 to 6.8 so the pH actually drops by 0.66. PoolMath thinks the pH goes down to 6.94 in the upper section to get to 128 ounces weight of dry acid so as Jason notes that's more accurate.
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