Matt,Matt said:Richard,
Are you essentially saying that the only reason we have any carbonates in our pool above 10ppm is that the rate constant of the reaction to form CO2 is so slow? Is it just a kinetics issue and not determined by the change in gibbs free energy of the entire reaction?
Matt
There are two reasons we have carbonates in most pools. First, is that they provide a pH buffer. Second, is that they enable saturation of the water with calcium carbonate (when calcium is also added to the pool water). The saturation of calcium carbonate protects plaster/gunite/grout surfaces from pitting (dissolving). One can have a lower TA and still have the water saturated if the CH or pH (or temperature) is higher.
The flip side of the carbonate portion (not the CYA or borates portion) of TA, however, is that higher TA and lower pH result in faster outgassing of carbon dioxide resulting in a faster rise in pH (or a slower decline, if acidic sources of chlorine are used).
And yes, the lack of equilibrium is due to the slow kinetics of carbon dioxide transfer between water and air.
Richard