Saturation Index

[urville]

I have obtained water balance. Thank you to everyone who helped me during my moment of panic and the days since.

I am still adding dichlor for daily chlorine until I get CYA up to 30.
FC - 4
PH - 7.6
ALK - 50
CH - 110

This question is about the saturation index.

So, in pool math when I plug in my numbers it warns me that my CSI is -0.38
Hovering over this number warns me:

Potential to become corrosive to plaster.

I have a Taylor 2006 test kit and in it is a Taylor Watergram.
When I dial in all my numbers the watergram concurs on CSI.
Only the watergram warns me:

Si of -0.3 or lower may be corrosive to concrete, plaster, or metal surfaces.

I just want to confirm these parameters are safe for my Intex portable spa. I could up my CH to 150, which does look like it would put me right over the line into balance.

 

[Richard320]

Your spa is vinyl. There's no Calcium in it to leach out.

 

[MPurcell]

Low CSI means that the water will likely pull calcium from surfaces that contain calcium. Your spa has no surfaces that contain calcium, so this is not an area you would need to be concerned about. The guideline for CSI is -0.6 to +0.6. When CSI is on the high side, near +0.6 you can get calcium deposits, which can cause problems with the equipment such as in the heater core, etc. You would be better to keep the CSI low within the acceptable range as that will keep the equipment from getting calcium deposits.

 

[pooldv]

More here, Pool School - Calcium Scaling