New China Shop Topic: How Accurate is the Pool Calculator?

[waterbear]

Acid and base demand cannot be calculated without a chemical test since they depend on other factors such as TA and temperature and how fast the chemical is added. (for example muriatic acid will have an almost instantaneous effect on pH while cyanuric acid, because of its slow dissolving nature, will not have a appreciable MEASURABLE effect since the slow drop in pH that occurs as it dissolves will be offset by the bicarbonate buffer in the water and the pH rise from outgassing of CO2 and the drop in TA that it will cause is going to be smaller than the precision of our TA test.)

A calculator like the pool calculator or a treatment table can only approximate how much of a pH rise or drop a certain amount of a chemical can cause that may or may not have ANY basis in reality! IF your pool is in what is considered a normal range of balance and temperature then the results can and will be off, particularly for large changes in pH. In fact, here is a direct quote from the pH section of the pool calculator:
Note: pH calculations depend on TA and Borate. Results are approximate and can be off significantly for large pH changes. Changing your pH will also change your TA.

IF you want a more precise way to determine how much of a chemical you need then do an acid or base demand test! (since base demand tests are set up for soda ash--sodium carbonate--it is lucky that twice the amount of borax by weight--sodium tetraborate decahydrate--produces about the same pH rise so you just need to double the weight of soda ash when substituting borax for pH increasing.