Saturation Question - Big CSI vs LSI mismatch

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thewalk

Member
Apr 5, 2025
7
Sacramento
Hi all, before diving into my question, I did find quite a few threads on this topic, but none had such a big difference between CSI and LSI (Taylor Waterwheel) that wasn't explained by some sort of calculation error. Maybe my issue is also some calculation error I am just missing. I know the waterwheel provides less different measurements and leaves out many parameters but the differences between the two are very different so I wanted to get some clarity, in particular, before adding calcium, which would push me further away from a 0 balance on the Waterwheel but near 0 on the CSI provided by Pool Math.

Measurements Today all with Taylor Kit and Goals:
temp 78 degrees F
FC 6.5 -> hold
pH 7.7 -> hold (range 7.6-7.8)
TA 80 -> hold
TH 400 -> plan to increase to 450...maybe even 500.
CYA 70-> plan to increase to 75
Salt 3100 -> added salt today to increase to 3300

Borates (based on test strips) 40 -> hold

On the pool math, the CSI for my goals amounts to -0.09 but on the Taylor Waterwheel I get almost +0.40. None of the other threads I read had this big of a discrepancy that wasn't explained by something else. The "further reading" post on this subjects states "Do not get hung up on the "which is better" debate, as that is a false choice. The indices are simply measures of how stable calcium carbonate is in solution. You can use one or the other; both will give you the same general answer." but its hard for me to not wonder which is "best" with such big differences.

In general, trying to aim for slightly positive in balance, hence my desire to push CA higher in the "ideal" calcium range. The owners before me seemingly added almost no calcium to the pool and there seems to be a lot of what I assume is corrosive damage to some of the rocks around my pool. But I am open to learning and suggestions!

Thanks in advance for any help.
 
Thanks both for your quick replies. I thought I had read to always use the direct Taylor Kit TA measurement. In retrospect, that must have just been for when filling out the pool math values which seem to make those adjustments for me. Adjusting for CYA and Borates on the Waterwheel brought the difference to less then 0.1 of a difference. So it was a calculation error on my part after all.

Why do you want to increase the CH?
What is the pH, TA and CH of your fill water?
Click to expand...

Some of the rocks in the pool area have corroded, I suspect because there was almost no calcium added when I moved in, probably for years. That said, I figured, perhaps incorrectly, I'd like to keep the calcium on the mid-to-high end of the "ideal range". Pool Math recommends 350-550ppm so I was targeting 450-500ppm. All other factors held the same, this would bring my CSI from -0.14 at CH of 400ppm to -0.05 at 500 ppm - both within acceptable ranges.

I am not sure the fill water. The autofill is broken and I have not had to manually add any since we moved in this past fall, between low losses from heat/use and the rainy season of Northern California. Since Jan, I have added 66 pounds of calcium chloride to get to ~400ppm, though some of that is probably dilution from the rainwater. Reports suggest tap water in my area is typically around 7.7-8.0 pH, <50 ppm calcium, and "low" alkalinity.
 
thewalk said:
Thanks both for your quick replies. I thought I had read to always use the direct Taylor Kit TA measurement. In retrospect, that must have just been for when filling out the pool math values which seem to make those adjustments for me. Adjusting for CYA and Borates on the Waterwheel brought the difference to less then 0.1 of a difference. So it was a calculation error on my part after all.



Some of the rocks in the pool area have corroded, I suspect because there was almost no calcium added when I moved in, probably for years. That said, I figured, perhaps incorrectly, I'd like to keep the calcium on the mid-to-high end of the "ideal range". Pool Math recommends 350-550ppm so I was targeting 450-500ppm. All other factors held the same, this would bring my CSI from -0.14 at CH of 400ppm to -0.05 at 500 ppm - both within acceptable ranges.

I am not sure the fill water. The autofill is broken and I have not had to manually add any since we moved in this past fall, between low losses from heat/use and the rainy season of Northern California. Since Jan, I have added 66 pounds of calcium chloride to get to ~400ppm, though some of that is probably dilution from the rainwater. Reports suggest tap water in my area is typically around 7.7-8.0 pH, <50 ppm calcium, and "low" alkalinity.
Click to expand...
Test your fill water and post results for pH, TA and CH.
In summer your evaporation rate will increase and require tap water to keep the pool level correct.
What is broken on the autofill?

Post a few pics of the rocks that are damaged.
 
Rock will deteriorate with water exposure no matter what you do. The CH of your water has little impact on that. Most cracking and spalling will be caused by water soaking into porous spaces, evaporating, and leaving behind crystals of dissolved minerals (calcium, magnesium, and sodium compounds). The crystals typically expand to a volume larger than the pore space and that creates pressure resulting in cracks. Absorbed moisture can also cause freeze/thaw damage to stones. I wouldn’t worry about it.
 
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