Focusing on Total Alkalinity
Rather than focus on pH, Jock found direct correlation between Total Alkalinity and Staining. Total Alkalinity measures carbonates. And carbonates turn metal compounds insoluble (see Alkalinity is the Problem and Solution on page…) Using empirical data from his service pools, he developed an algorithm to predict staining based on Total Hardness. He chose Total Hardness since it includes hardness beyond simply calcium hardness.
For Plaster: f(TH)=-20ln(TH)+195, for Non-Plaster: f(TH)=-20ln(TH)+185
Where f(TH) is the Total Alkalinity staining threshold.
Note: the difference in surface is that plaster contains carbonates that are released into water.
This gave a way to predict staining in a much linear fashion. Simply put, when the actual Total Alkalinity exceeds the threshold Total Alkalinity, probability of staining increases dramatically. When these values are equal, staining may occur. However, as long as the actual Total Alkalinity stays below the threshold, staining is avoided. We can use a similar format to the LSI to express this.
f(TH) = TAthreshold,
- If TAactual – TAthreshold > 0, water will be supersaturated; staining likely to occur
- If TAactual – TAthreshold = 0, water will be saturated; staining may occur
- If TAactual – TAthreshold < 0, water will be undersaturated; staining unlikely to occur
With insight into the correlation between Total Alkalinity, Total Hardness, and Staining, we then need to address pH.