Calcium Carbonate Precipitation Potential using PoolEquation

[smallpooldad]

Using the "PoolEquations" Excel spreadsheet I am trying to determine what would the "Calcium Carbonate Precipitation Potential" be if the numbers looked as follows:

Cl 5
pH 7.3
TA 120
CH 475
CyA 80
Salt 3200
Borates 50
Orthophosphates 2000 (ppb)
Temp at present 78F (to max 84F and an average of 81F)
Carbonate Alkalinity (ppm CaCO3) 92.0
CSI -0.18
LSI -0.09

Is the "Calcium Carbonate Precipitation Potential" number OK or should one or more of the above be adjusted, and if so to what figure(s)?

Thank you.

 

[chem geek]

Re: Calcium Carbonate Precipitation Potential using PoolEqua

I used 3734 ppm TDS to get the salt level at 3200 ppm. The rest of the TDS is calcium, bicarbonate and boric acid. I get a CSI of -0.21 so basically similar to your number. If I click on the Calculate CCPP button I get a CCPP of -11.2

The Calcium Carbonate Precipitation Potential (CCPP) is normally used when the CSI is positive to determine how much calcium carbonate can potentially precipitate. As it precipitates, the pH and the CH drop so accelerate stopping this precipitation. It's essentially a measure of capacity. It is not a measure of rate.

When the CSI is negative, the CCPP tells you how much calcium carbonate can dissolve (say, from plaster) before such dissolving stops. So I don't think it's very useful to look at when the CSI is negative, especially when the CSI is only a little negative. At any rate, it just says that your CSI isn't so negative as to cause problems with plaster, but you already knew that from the CSI number itself.