CSI result different using Taylor kit vs. Pool Calculator

[singerteacher]

Well, I was starting to worry that my CSI was too high at 0.45 according to the circular dial calculator that came with my Taylor 2006 kit, which cautions against CSI over 0.5, so I'm getting close. But then I plugged the same numbers into The Pool Calculator and got a CSI of 0.39, which says I don't have to worry about it until it's over 0.6. I'm confused.

Why are they different, or is this difference really not that much? If it's important, which one is correct? Also: could this be the result of not enough salt in my water softener?

Thanks for your expert input!

 

[chem geek]

The Taylor Watergram does not take into account Total Dissolved Solids (TDS) and probably assumes around 500 ppm. So it will read up to 0.2 higher compared to putting a high TDS (say, 3000 for an SWG pool) into The Pool Calculator. The Pool Calculator uses an approximate formula, but it's only (usually) too high by around 0.02 or so compared to Taylor if you use 500 ppm for TDS.

As for when a higher CSI is a problem, it partly depends on the pool. Pools with SWG systems should not have as high a CSI since there will be scaling in the SWG. This is also somewhat true for pools with a gas heater. If you notice that your water is a little cloudy, then it could be due to the higher CSI.

As for why your CSI is on the high side, you'd have to post a full set of numbers to see what's happening.

Richard