CH and TA high...what will this do?

[Blivit79]

According to pool math, I needed to raise my CH and TA levels. I bought calcium chloride and baking soda to do so. I do not own a scale for the powders so instead I bought amounts that were around double what I needed. I marked the level on the outside of the container then split it in half and marked that amount as well. I then added until the level was to my half mark.

I let everything circulate for roughly 1 hour and remeasured. Both CH and TA did raise, but went above what I was targeting. I wanted to raise CH from 250-300 and TA from 50-90. I instead ended up at CH of 350 and TA of 120, measured twice to confirm. All of my other levels are good (FC 5, PH 7.5, CYA 45-50) and the water is clear. The pool is gunite. Do I need to be concerned with elevated CH and TA levels? With these values pool math has my CSI high at 0.5 and another source has my LSI at 0.6. I am not too familiar with how CSI/LSI correlate.

 

[Texas Splash]

With an IG plaster pool, you certainly want to be conscious about those levels, to include pH as the 3 of them tend to enhance some issues when one is off. Fortunately, the TA is easy to fix - acid. That will of course also help lower your pH. If you find your pH getting to low (7.2) and the TA still needs to be lower, you can take pH to about 7.0 then aerate to raise the pH naturally while keeping the TA lower. We typically advise owners to let the TA go down a bit if it works well for the pH. Yours was previously at 50, but even 60-70 might be good for your pool. Something to consider for next time.
As for your CH, the only way to lower is water exchange. If you're at 350 now, that's not the worst thing to happen, just make sure you don't add anything else in the future that may contribute to high CH (i.e. Ca-Hypo). I would continue to tinker with the calculator and try different pH and TA adjustments with your new CH level to see how that may adjust the CSI more in your favor.

 

[Blivit79]

With an IG plaster pool, you certainly want to be conscious about those levels, to include pH as the 3 of them tend to enhance some issues when one is off. Fortunately, the TA is easy to fix - acid. That will of course also help lower your pH. If you find your pH getting to low (7.2) and the TA still needs to be lower, you can take pH to about 7.0 then aerate to raise the pH naturally while keeping the TA lower. We typically advise owners to let the TA go down a bit if it works well for the pH. Yours was previously at 50, but even 60-70 might be good for your pool. Something to consider for next time.
As for your CH, the only way to lower is water exchange. If you're at 350 now, that's not the worst thing to happen, just make sure you don't add anything else in the future that may contribute to high CH (i.e. Ca-Hypo). I would continue to tinker with the calculator and try different pH and TA adjustments with your new CH level to see how that may adjust the CSI more in your favor.

Thanks. I was going by the recommended levels section and that lists CH 250-350 and TA 70-90+. I thought TA was used to basically stabilize PH and the higher the number the more it would do so. Having TA lower 60-70 would that mean I would have to keep the PH lower as well?

I am playing around with the calculator and it seems if I lower both TA and PH it will bring my CSI down. I will try to aerate.

 

[Texas Splash]

Yes, every pool is different. And while there is a recommended range for TA, some of us find that our pH remains more stable it we allow the TA to be slightly above or below that range. The pH is more important in that relationship. So whether your TA is 70, 90, or 120, which ever one helps keep your pH in the mid-7 better is most important. Watching your CSI helps too.

 

[chiefwej]

Actually the CSI is the most important number. As far as high CH and high TA I have some experiance in that because my fill water has both and with the insane evaporation rates here in summer they are very hard to control. I recently spent an entire season with a CH over 1,000 before draining and getting it back down to the 350-400 where it starts. My TA starts out around 150 or so, but at least there is a way to lower that one. (Although with my fill water and evaporation rate it just bounces back up in a few days)

You can just use acid and aeration to lower the TA, while keeping a very close eye on the CSI. As long as you are not "blessed" with a combination of rapid evaporation and high TA in the fill water, you should be able to find the sweet spot where your PH stays balanced and the CSI is in a safe range.

The CH tells you how much calcium is in the water. The CSI tells you (when high) if it will stay in the water or precipitate out as scale on the pool, or if (too low) the water is aggressive and will actually dissolve calcium right out of the plaster and grout damaging the pool. CSI is calculated from several factors, (pH, CH, TA, Temp, etc.) of these the one you have the most direct control is pH.

 

[JoyfulNoise]

Thanks. I was going by the recommended levels section and that lists CH 250-350 and TA 70-90+. I thought TA was used to basically stabilize PH and the higher the number the more it would do so. Having TA lower 60-70 would that mean I would have to keep the PH lower as well?

I am playing around with the calculator and it seems if I lower both TA and PH it will bring my CSI down. I will try to aerate.

Carbonate alkalinity (the main component of TA) is BOTH a pH buffer (helps resist changes to pH) AND a source of pH rise. The higher your TA, the greater the amount of dissolved bicarbonate ion in solution. Bicarbonate converts into dissolved CO2 and it is the process of dissolved CO2 out gassing from water that causes the pH to rise (when bicarbonate converts to CO2, it consumes a hydrogen atom).

So while it is true that a greater TA will cause a greater resistance to the pH dropping (carbonates have greater buffeting capacity for acidic additions) it is also the case that higher TA can lead to more rapid pH rise. Therefore you need to adjust your TA (up or down but for most people it's down) so that your pH is stable.


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[Richard320]

First impression: your pool is not as big as you think it is.

Second thought: You should be able to get a better handle on its size when you start adding acid and aerating to lower TA. Just lowering the TA will reduce the CSI. 350 CH is lower than my pool has ever been in the five years or so I've owned it. Just because it's slightly above some "ideal" doesn't mean it's a problem.

What you want to do is plug your numbers into poolmath. See what it calls for to lower pH. Then go down to the bottom where it says Effects of Adding Chemicals and see what that says will happen when you add that amount of acid. The pH will only be an approximation, but the TA should be very close. If needs be, target a slightly higher pH so you get a nice even TA drop that is a multiple of 10. Add that amount of acid. Did the TA drop the expected amount from Effects of Adding Chemicals? Did the pH only drop to the level you targeted? Did you overshoot or undershoot? Adjust the pool volume up top on poolmath accordingly. Over a period of a few weeks, you'll be able to zero in on a number that reacts precisely as poolmath says it will, and then you'll know your pool volume.