Borates, pH Impact to CSI

UtexasChris

Well-known member
Jun 10, 2020
67
Austin, TX
Hi All,

I've looked at all the guidance here on TFP and focused on keeping my chemistry in range using PoolMath. However, it seems while I'm in range with the TFP recommendations, my CSI is highly negative.

For example, here are my readings:

FC 5
pH 8.2
TA 60 (2 weeks ago)
CH 500 (15 days ago)
CYA 70 (17 days ago)
Salt 3450
BOR 48 (14 days ago using Mannitol method)
Water Temp 66
CSI -.37

I usually won't let the pH get above 7.8 or 8.0 at the most before I chase it down to 7.2 or 7.3 using muriatic acid as that's my understanding of the TFP recommendation. I let the pH climb a little higher as the water is a good 15 degrees colder with the cold weather in Austin right now and the cold water seems to make pH go further negative.

That said, if I push the pH down to 7.2 (using liquid muriatic acid) with the stats above, it says my CSI would be -0.77 which seems troubling. When I check the impact of zero'ing out the Borates (using poolmath), the CSI swings from current -0.37 the way to 0.18.

Should I be allowing the pH to rise more instead of pushing it back down with acid? Won't it cause scale if I allow pH to go higher? I would greatly appreciate thoughts, suggestions, and recommendations.
 
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ajw22

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There is no TFP recommendation to push your pH down to 7.2 other then when you are trying to lower your TA.

Run your pH in the 7.8-8.0 range. Don't lower your pH below 7.6.

CSI between +0.6 and -0.6 is ok. +0.3 to -0.3 is ideal. A CSI down to -0.6 is ok during the winter when cold water will lower the CSI.
 

UtexasChris

Well-known member
Jun 10, 2020
67
Austin, TX
Thanks, @ajw22 I clearly must have misread a thread somewhere. I’ll start running between 7.6 and 8.0 and see how often I’m having to add acid as I suspect it will be every other day.

If I key in 7.6pH in PoolMath, it’s still coming up with a CSI of -0.47. Doesn’t that seem too far negative or should I stop being concerned?
 

ajw22

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Thanks, @ajw22 I clearly must have misread a thread somewhere. I’ll start running between 7.6 and 8.0 and see how often I’m having to add acid as I suspect it will be every other day.

If I key in 7.6pH in PoolMath, it’s still coming up with a CSI of -0.47. Doesn’t that seem too far negative or should I stop being concerned?

It will be fine. As you observe the pH does not stay at 7.6 for very long.
 

mknauss

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Your TA is primarily comprised of CYA and BOR alkalinity. Your pH should not rise that quickly. Are you running your overflow on the spa all the time?
 

mknauss

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Your carbonate alkalinity is only in the low 20's with a TA of 60, CYA of 70, and BOR of 50. I would think the pH should stabilize at not much more than 8, unless it is getting vigorous aeration or high TA fill water is being used on a regular basis.
 

UtexasChris

Well-known member
Jun 10, 2020
67
Austin, TX
Should I consider raising the TA to reduce the negativity of the CSI? Here are my most current readings:

FC: 7
pH: 8.0
TA: 60
CH: 460
CYA: 80
Salt: 3350
BOR: 44
Water Temp: 60
CSI: -.42

Using poolmath, an increase in TA from current 60 to 80 would change my CSI value from -0.42 to -0.07. When I reduce pH to 7.6 with acid, it would only bounce to -0.36 vs my current setup where CSI drops to -0.60 when I drop the pH to 7.6.

If the goal is to play with inputs within the guide ranges to get a better CSI, this would seem to the right play. Anything I should consider before taking this approach?
 

mknauss

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If your pH is 8, leave it. Do not reduce it. The lower water temperature is pushing your CSI lower.

If you add some carbonate alkalinity (via baking soda), your pH will rise. You can try adding no more than 20 ppm TA worth of baking soda.
 

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UtexasChris

Well-known member
Jun 10, 2020
67
Austin, TX
If your pH is 8, leave it. Do not reduce it. The lower water temperature is pushing your CSI lower.

If you add some carbonate alkalinity (via baking soda), your pH will rise. You can try adding no more than 20 ppm TA worth of baking soda.

My understanding was I should not let the pH get much higher than 8 to avoid scale. In order to do this, I would add acid to move it down to 7.6 and then ride it up again as long as I can while ensuring it doesn't stay north of 8 and repeat.

Just to make sure I understand your comment on the lower water temperature pushing CSI down, are you saying that the potentially damaging characteristics of a -0.6 CSI are not as great if a major variable driving it is water temp? I want to make sure I'm thinking about this the right way as I just looked at it as an equation that spits out a number where the number is absolute based on the inputs.

If I were to use baking soda and pH rises, this is a one time event that I would then just offset with acid, correct? I appreciate all of your guidance.
 

mknauss

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CSI is more important than higher pH. A pH of 8 is just fine.

If you add baking soda, and then add acid, you remove the alkalinity you added via the baking soda.

When water temperature falls, the best thing to let balance that is pH. So letting it be at 8 or even 8.2 will not create any issues. When the water warms, then you need to address it. Again, manage the CSI.
 

Bperry

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Depending on where you are, adding CH can also help. I bumped my CH up a bit when I drained mine for the winter knowing that I’ll get a huge downpour or water over the winter so by the time it warms up, the CH won’t be as high.
 

jseyfert3

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My understanding was I should not let the pH get much higher than 8 to avoid scale. In order to do this, I would add acid to move it down to 7.6 and then ride it up again as long as I can while ensuring it doesn't stay north of 8 and repeat.
Scaling can form when the CSI of the water is positive. If your pH is 8 or even higher, but the CSI is negative, you won’t get scaling. pH plays a major role in calculating the CSI, but it’s the CSI that indicates whether scaling is possible, not the pH.
 

Bperry

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I’m not 100% certain, my understanding is you don’t want to let it go way into the 8’s but I could be wrong.
I think the trouble is when it gets over 8.2 the pH is difficult to accurately measure unless you have an electronic meter. Even those can be flaky though. So keeping it in a range that you can test accurately is an important detail. If it stays naturally at 8 or even 8.2, I’d think it’s ok as long as the csi was in proper range.