Saturation Question - Big CSI vs LSI mismatch

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T

thewalk

Member
Apr 5, 2025
8
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.
 
proavia said:
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.
Click to expand...
IMG_4410.jpgIMG_4411.jpgIMG_4412.jpg

Here are a few pictures. We have some similar deterioration out front, so JoyfulNoise's assessment is probably correct. Also, it seems to have only affected the exterior rocks that kids may have been climbing on over the years.

Earnest question, what is the utility of testing the fill water since, I imagine, I will have to retest the pool water after a major refill or 1-2x per week anyway? I can test easily enough, I am just trying to figure out what that would change in my chemical balancing management.

The autofill is a curious situation. We tested it with the walk-through, and it worked, and we were told that the flowmaster was "just replaced." After we moved in, the autofill no longer releases water (but did during the inspection). There is also an outdoor kitchen area where the sink not longer releases water. I believe this anti-siphon valve is feeding the line that goes to the outfill and the outdoor kitchen sink, and I think it is defunct. Haven't had the time to replace it yet.
JoyfulNoise said:
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.
Click to expand...
Thanks! You are probably right. Though we don't get freezing weather, we do get some harsh conditions sometimes, and we have similar rocks in the front of the house that have corroded. So sounds like no strong reason to increase CH within the "ideal range" other than may for overall CSI balance?
 
thewalk said:
Earnest question, what is the utility of testing the fill water
Click to expand...
It dictates if its wise to add CH manually. You have more evaporation in Sacramento than rain so if your fill water is high TA or CH it will raise either level in the pool.

If you have low CH fill water, you can keep the pool CH a little on the high side and rain will eventually dilute it. With 18 inch annual average rainfall, it'll take a hot minute, but it'll happen.

It will also give us an idea if the TA will remain stable or rise. If the TA gets above 100 it starts pulling the PH up faster.
 
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