Carl,

The two charts have a relative scale so the absolute units aren't meaningful. Nevertheless, the first chart of relative CO2 outgas rates has a base unit of 0.0 meaning no outgassing with the normal equilibrium amount of CO2 in the water as there should be when exposed to air. A unit of 1.0 means twice the amount of CO2 dissolved in the water as would normally be there from equilibrium with the air. So if you add 1 to the numbers in the chart, then that represents the factor of how much more CO2 is in the water than there should be if in balance with the air. The more out of balance, the faster the outgassing -- if the number in a cell is twice the number in another cell, then the outgassing should be twice as fast (all else equal).

The second chart is even harder to fathom since there isn't even a meaningful base unit in this case except that 0.00 means no pH rise at all. It is still true that a cell that is twice the number in another cell does mean that the rate of pH rise will be double, but the chart doesn't tell you how much that is in absolute units (I put in numbers that are roughly in pH rise ranges, but that's just an arbitrary scaling).

So the two charts are really just "tendencies" and the color coding is an attempt at giving rough areas of stability (green), rising pH and requirement of acid addition (red) and intermediate levels in orange, but this is very, very rough since aeration can make even some green numbers not be very stable (in an SWG environment, for example).

Jim,

I'm just wondering why you saw such a pH rise even at relatively normal TA levels. Does your pool have any aeration features such as waterfalls, spillovers, fountains, etc.? I'm guessing there isn't since it's an above ground pool. Or has there been summer rain (raindrops aerate the water when they splash)?

Richard