We don't know the cause of the CH rise (or not dropping when it should from dilution). It does sound like you are seeing something similar to what I saw. Have you noticed an increase in the rate of pH rise and required acid addition that occurred around the same time as the CH didn't drop as expected? If so, then that would imply dissolving of calcium carbonate (or calcium hydroxide, though that's less likely unless it was trapped under calcium carbonate). If it's just a CH change you are seeing and nothing else is out of the ordinary (i.e. no unusual pH rise, assuming you are using a hypochlorite source of chlorine), then there might be something in the water giving a false high CH reading, but I've been looking into that and don't see anything obvious yet (false low readings can occur from co-precipitation of calcium with magnesium and this is avoided by adding most of the titrant drops first, taking two passes if necessary).
Strange Test Results with High CH
- Thread starter chem geek
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My pH rise has been consistent over the last 6 month or so. I add about 30 oz. of MA every five days. I don't really notice a CH increase. I just know that my CH should have dropped when my salt, borates, and CYA levels dropped by around 40% after several heavy rains this winter/spring. During that same time my CH remained at 475-500. Seems strange to me.
HouTex, perhaps you have already considered this; it would be typical for the salt, borates, and CYA, to lower due to tap water not containing them. But tap water does contain calcium. Therefore, it would make sense that the calcium level would not lower as much as the other constituents.
There is also one more possibility, we are learning through experiments that plaster that has a high water/cement ratio, and a high content of calcium chloride, will over time, continue to dissolve calcium out from the plaster matrix. And it not due to the water being aggressive. Calcium chloride is very soluble, to the tune of about 300,000 ppm! Also, plaster that contains a lot of calcium chloride shrinks and causes micro-cracking, thereby allowing water to pentrate into the plaster matrix and also dissolving calcium hydroxide. Same result; calcium increases in the water, plus the pH rises more.
It has occurred to me that Langelier probably didn't study or experiment with cement/concrete that contained calcium chloride and high water/cement ratios.
There is also one more possibility, we are learning through experiments that plaster that has a high water/cement ratio, and a high content of calcium chloride, will over time, continue to dissolve calcium out from the plaster matrix. And it not due to the water being aggressive. Calcium chloride is very soluble, to the tune of about 300,000 ppm! Also, plaster that contains a lot of calcium chloride shrinks and causes micro-cracking, thereby allowing water to pentrate into the plaster matrix and also dissolving calcium hydroxide. Same result; calcium increases in the water, plus the pH rises more.
It has occurred to me that Langelier probably didn't study or experiment with cement/concrete that contained calcium chloride and high water/cement ratios.
Thanks onbalance. I think the CH must be coming from my plaster. As I said earlier in the thread, I've hardly had to top up my pool with tap water over the last 5 months (and my tap water is 150 CH) due to frequent rains here in SE Texas. Yet my CH has stayed in the 475-500 range while my salt, borates, and CYA levels have all fallen substantially over the same period.
I also have a few of these small white dots on the bottom of my pool that look like miniature volcanos. I've reviewed some stuff I've found on line (some of it I think from links you've posted--thanks) and it seems they also are caused by a bad plaster job and/or mixture.
But on the whole I'm not unhappy with the look of my plaster. It's only in low light that you can see the etching.
I also have a few of these small white dots on the bottom of my pool that look like miniature volcanos. I've reviewed some stuff I've found on line (some of it I think from links you've posted--thanks) and it seems they also are caused by a bad plaster job and/or mixture.
But on the whole I'm not unhappy with the look of my plaster. It's only in low light that you can see the etching.
I prefer the term "leaching" rather than "etching" because balanced water will leach soluble calcium compounds from a plaster surface, as opposed to aggressive water etching the surface. And those spots are porous, not etched.
If the bottom of your pool has white dots that look like miniature volcanos, which means they are probably "calcium nodules," then you need to call your plasterer and tell them that their new plaster finish is probably losing its' bond (debonding) to the underlying substrate and is also called delaminating. Should be a warranty issue. In time, your plaster surface will probably begin to "break off" in large chunks and expose the under-surface. That is not something you want to happen. And you shouldn't have to pay for fixing that. And again, the cause of delaminating is not from improper water chemistry. Calcium nodules are just a symptom of the underlying cause. Proper water chemistry cannot prevent them. If you go to poolhelp.com and click on "onBalance" you can find a link on "calcium nodules" and learn the mechanics of how and why nodules form.
If the bottom of your pool has white dots that look like miniature volcanos, which means they are probably "calcium nodules," then you need to call your plasterer and tell them that their new plaster finish is probably losing its' bond (debonding) to the underlying substrate and is also called delaminating. Should be a warranty issue. In time, your plaster surface will probably begin to "break off" in large chunks and expose the under-surface. That is not something you want to happen. And you shouldn't have to pay for fixing that. And again, the cause of delaminating is not from improper water chemistry. Calcium nodules are just a symptom of the underlying cause. Proper water chemistry cannot prevent them. If you go to poolhelp.com and click on "onBalance" you can find a link on "calcium nodules" and learn the mechanics of how and why nodules form.
Well, my pool is still acting a bit strangely. We were gone for 3-1/2 weeks on a combination vacation and business trip and have someone staying at our house who added chlorine to the pool. I knew that the pH would rise somewhat, but I left with it at 7.5 and when I came back it was above 8.0 where the acid demand test needed the equivalent of 10 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to get the pH back down (which I've done). I have 50 ppm Borates in the pool as well. So that was surprising since 1) the amount of chlorine added was less than usual since the water temp was kept lower closer to 80ºF (the added rate was around 0.6 ppm FC per day average), 2) the pool was not used every day, 3) I have an electric mostly opaque pool safety cover on the pool when not in use and 4) the TA is fairly low at or just below 70 ppm (when measured at pH 7.5). The pool looked great upon return and chlorine measurement was fine, but the pH was quite high.
So I think I can pretty much rule out the pH rise being mostly from carbon dioxide outgassing and having it rise a lot even with less chlorine usage implies that it probably isn't all from the chlorinating liquid either. This upcoming weekend I'll do more tests including CH which was at 500 ppm before I left (I made it higher since I have the TA lower). If the CH is higher, then the pool is behaving as if calcium hydroxide or calcium carbonate is dissolving into it. The two can be distinguished based on whether the TA is higher after adjusting the pH downward.
So I think I can pretty much rule out the pH rise being mostly from carbon dioxide outgassing and having it rise a lot even with less chlorine usage implies that it probably isn't all from the chlorinating liquid either. This upcoming weekend I'll do more tests including CH which was at 500 ppm before I left (I made it higher since I have the TA lower). If the CH is higher, then the pool is behaving as if calcium hydroxide or calcium carbonate is dissolving into it. The two can be distinguished based on whether the TA is higher after adjusting the pH downward.
I just did a full set of measurements today with FC 5.0, CC <0.2, pH 7.9, TA 90, CH 490, CYA 40. Acid demand test shows 6 cups of acid getting down to 7.6 pH and dropping TA from 90 to 80. The good news is that the CH does not seem to be increasing so would eliminate either calcium carbonate or calcium hydroxide dissolving (though we're talking within 10% so test error is still a possibility so CH could in fact still be rising). The rise in pH and TA act as if sodium carbonate has been added to the pool along with carbon dioxide outgassing. Had the CH increased, then 50 ppm of calcium carbonate would roughly explain the results.
It has been extraordinarily windy recently and this has lowered the pool temperature overnight by almost double the rate of normal for summer so when the pool is in use that extra wind could lead to a faster rate of carbon dioxide outgassing, but though that could explain a rise in pH it doesn't explain the rise in TA. If only carbon dioxide outgassing were occurring, then the acid additions would result in a lowering of TA over time, but the opposite is happening.
I've double checked that the auto-fill isn't constantly on indicating a leak and that should dilute CH and CYA anyway which isn't happening (the fill water has 80 ppm TA so could explain an increase in TA if evaporation/refill were the cause).
So the rise in pH and TA (and over the winter, CH not dropping) are still a mystery unless there is something in the chlorinating liquid that is all I have been adding (other than Muriatic Acid). The manufacturer says nothing has changed in their processes and that the pH from excess lye is the same as before. Also, over the winter very little chlorine was added and the pool was kept covered and not used. I'll keep track of how things go over the summer season and hopefully solve this mystery.
It has been extraordinarily windy recently and this has lowered the pool temperature overnight by almost double the rate of normal for summer so when the pool is in use that extra wind could lead to a faster rate of carbon dioxide outgassing, but though that could explain a rise in pH it doesn't explain the rise in TA. If only carbon dioxide outgassing were occurring, then the acid additions would result in a lowering of TA over time, but the opposite is happening.
I've double checked that the auto-fill isn't constantly on indicating a leak and that should dilute CH and CYA anyway which isn't happening (the fill water has 80 ppm TA so could explain an increase in TA if evaporation/refill were the cause).
So the rise in pH and TA (and over the winter, CH not dropping) are still a mystery unless there is something in the chlorinating liquid that is all I have been adding (other than Muriatic Acid). The manufacturer says nothing has changed in their processes and that the pH from excess lye is the same as before. Also, over the winter very little chlorine was added and the pool was kept covered and not used. I'll keep track of how things go over the summer season and hopefully solve this mystery.
I'm tracking things this swim season and will post the latest results in a couple of months, probably in October. I want to give enough time for the effects to be obvious (such as CH rise, if any).
So I did a full set of measurements today and got FC 5.0, CC <0.2, pH 7.8, TA 90, CH 510, CYA 45, (Salt went from 1480 to 1680).
So the behavior is as if the required acid additions are mostly due to offsetting a strong base such as excess lye in chlorinating liquid and bleach. The CH went up a little, but within measurement error. Salt went up as expected between the chlorine and acid additions and showed that there was little water dilution which is expected since I have a cartridge filter I only need to clean once a year. The similar TA at a similar pH shows that the pH rise isn't from carbon dioxide outgassing (since the TA would drop over time in that case, due to the acid additions) unless there was substantial evaporation and refill (which adds to TA and some CH), but with a pool cover on most of the time that seems unlikely.
It's too bad I don't have a pH test that would work with the chlorinating liquid. The 12.5% chlorinating liquid is supposed to have a pH of around 12.5 for 0.25% sodium hydroxide, but perhaps it's actually more this year for some reason (though when I talked to Hasa they said that was not the case).
So the behavior is as if the required acid additions are mostly due to offsetting a strong base such as excess lye in chlorinating liquid and bleach. The CH went up a little, but within measurement error. Salt went up as expected between the chlorine and acid additions and showed that there was little water dilution which is expected since I have a cartridge filter I only need to clean once a year. The similar TA at a similar pH shows that the pH rise isn't from carbon dioxide outgassing (since the TA would drop over time in that case, due to the acid additions) unless there was substantial evaporation and refill (which adds to TA and some CH), but with a pool cover on most of the time that seems unlikely.
It's too bad I don't have a pH test that would work with the chlorinating liquid. The 12.5% chlorinating liquid is supposed to have a pH of around 12.5 for 0.25% sodium hydroxide, but perhaps it's actually more this year for some reason (though when I talked to Hasa they said that was not the case).