In ideal world Carbonate Alkalinity (ppm CaCO3)?

[smallpooldad]

In an ideal world what would be an ideal Carbonate Alkalinity (ppm CaCO3)?

I realize that ones other numbers should be within the normal ranges and that would affect the answer but if were a perfect world what would be the perfect number, 100? Or is this a silly question, or if it depends on something does it depend on what a person is trying to acheive?

And why is it recommended to keep the alkakinity in a SWG pool between 60-80 ppm?

Thank you to those that answer.

 

[chem geek]

There is no single correct answer because one of the primary purposes for carbonate alkalinity is to saturate the water with calcium carbonate to protect plaster surfaces. The saturation level of calcium carbonate depends on pH, carbonate alkalinity, calcium hardness, and temperature. The carbonate alkalinity can be calculated from Total Alkalinity (TA) adjusted for Cyanuric Acid (CYA) (and for Borates, if present). All of this is done for you automatically when you enter numbers into The Pool Calculator.

The other factor to consider for carbonate alkalinity is that a higher amount causes more carbon dioxide to outgas faster and that causes the pH to rise (all else equal and assuming no net acidic sources of chlorine). SWG pools tend to rise in pH more than non-SWG pools so keeping a lower carbonate alkalinity lowers the rate of pH rise from carbon dioxide outgassing. You could readily have a lower carbonate alkalinity in a non-SWG pool as well if you wanted to and just compensate for the saturation index with a higher CH or perhaps higher pH target.

You want a certain minimum carbonate alkalinity to provide some pH buffering, but that can be fairly low (say, 40 ppm) if you are using hypochlorite sources of chlorine and don't have large chlorine swings or if you have 50 ppm Borates which also buffer pH.

 

[smallpooldad]

Chem Geek,

That answer was very clear. I need to maintain the SWG pool at a pH of 7.4 to control iron precipitation, so this information really helps. I might up the CH a bit from 350 to keep it in balance.

Aloha.