Csi Index, How Import Is It?

[timchase01]

Hi All,

I've had my new spa for about a week now, and using Nitro's info on lowering the TA and running the pumps to bring up the PH, I've got my water to be stable as follows:

PH: 7.6

TA: 70ppm

CH: 170ppm

Borate: 50ppm

Temp: 100

Based on this the pool calculator says my CSI is -0.12. So my question is how important is it to get to that magical 0.00? Am I going to have problems because of being at -0.12? Should I raise my CH up to get closer to 0?

Thanks to all for the great information that I've been able to find here!!!

Tim

[mcw53]

Hey Tim,

Your numbers look great. Assuming you have a fiberglass or acrylic spa, having a slightly negative CSI is not an issue. I typically target a CSI of around -0.10 to -0.20 to ensure I don't have any scaling issues.

[quantumchromodynamics]

If there is any plaster or grout, the CSI is very important. Cement will dissolve if the CSI is negative and scale will form if the CSI is excessively positive. If there is plaster, grout or other cement-based material, then the CSI should be kept as close to zero as possible without going negative.

If there is no plaster, grout or other cement based material, then it's only important not to go excessively positive, to avoid scaling. Due to high temperatures in the heater, the CSI will be higher in the heater than in the ambient water. If there is no plaster, grout or other cement based material, then the CSI should be kept less than zero to avoid scaling.

As far as metal corrosion (an oxidation process) is concerned, the primary factors are pH and oxidizer levels. Make sure to maintain a pH above 7.2 at all times, and avoid excessive chlorine or bromine levels. Maintaining lower, but very consistent chlorine levels is better than having to shock on a frequent basis. Adding cyanuric acid to the water will moderate the reaction rate of chlorine and reduce oxidation.