Can very high CH levels lead to pH rise?

[lalittle]

Is it possible for high Calcium Hardness levels to cause pH rise either directly or indirectly? I've been fighting with steady pH rise for a few years now, and it appears that my CH may be around 1000, which is significantly higher than most people hit. I'm wondering if this may be leading to some sort of out-of-balance situation that ends up manifesting as pH rise. My pH goes up by about 0.2 a day or so -- enough that I have to add about a half gallon twice a week (a little less) in order to keep it in check (between 7.8 and 7.2.) I noticed on the Taylor "Watergram" wheel calculator that with such high CH, the saturation index goes out of range when the pH hits 7.8 (i.e. to about -0.7, which is beyond that -0.5 recommended limit.) How much of a "problem" is this, and could this in some way be connected to my pH rise?

I compare my situation to my neighbors, and they rarely add acid -- almost never in some cases. My pool was re-plastered about 4 years ago, so the plaster is not new. The acid demand drops a bit during the winter months, but it still requires regular acid additions.

Note that when I say my CH "may" be about 1000 I mean that its not all that easy to test due to a preponderance of pink blobbies in the water during the Taylor test. I've followed the recommendations here and on Taylor's site for reducing this problem, but the "pinkness" of the actual liquid is so pale that it makes me question when the change to blue is "really" occurring. The only "obvious" change is when I hit 40 drops (i.e. 1000 CH), but at this point the pink blobbies are also turning blue, and I'm not clear if this means I've gone too far. My best guess, however, is that my CH is 1000, and my fill water is about 100. I recently replaced about 15 inches of water, which I figure is about 25% of the pool, so the CH was even higher before.

If I can get my CH down a bit it will help put the Watergram into the acceptable range, but I'm not clear how important this is, or if this is related to the pH rise. I can drain some and refill again to get the CH down further (as well as the CYA), but if it won't help me all that much, I'd prefer to save the money on water.

Here are my specs:

22K gallon non-SWG in ground pool.

FC (range) - 4.5 to 10.5 (5.5 at the moment - when FC reaches 4.5 to 5, I add a gallon to bring it to about 10 to 10.5.)
CC - negligible
pH (range) - 7.2 to 7.8 (7.6 at the moment)
TA - 50 to 60
CYA - 60 to 70
CH - 1000

I seem to have some borates in the pool based on the Lamotte test strips, but it's hard to tell because I'm not very unfamiliar with this test, and there isn't much definition between the colored squares. In other words, I am not completely confident about the results. When I compare the pool to the fill water using the strips, however, the color is a bit different, so it appears that there may be at least "some" borates in the pool.

For chlorination I use liquid Cl (mainly Hasa 12.5%.) (I stopped using pucks a while back.)

Thanks for any feedback on this,

Larry

 

[chem geek]

We don't know of any mechanism that has a high CH cause any sort of pH rise. At the extreme where a high CH possibly with a high pH and TA cause calcium carbonate to precipitate or scale, then that would actually lower the pH.

Your neighbors are likely using acidic sources of chlorine, such as Trichlor tabs, so in fact they ARE adding acid, but just doing so via the type of chlorine they are using.

As for pH rise, don't try and lower the pH below 7.5. Carbon dioxide only outgases more quickly at lower pH. See this table showing how over-carbonated pool water is compared to air at various pH and TA levels. In your situation, at a pH of 7.2 your water is over-carbonated by over a factor of 7 while at pH 7.5 it's just over a factor of 4 and at 7.8 it's less than a factor of 2. So the pH should be pretty darn stable near a pH of 7.8. If it's not, then something added to the water is having the pH rise, though I'm not sure what that is. I'd first just not worry about the pH unless it gets above 7.8 and then don't lower it below 7.5.

 

[lalittle]

I'm trying to keep the maintenance down, and lowering it from 7.8 to 7.5 will mean that I'll have to add acid almost every day. I'd like to increase that period by as much as possible (it's 3 days at the moment), and it makes things easier to add acid in half-gallon increments. That, however, would mean letting go above 8.0 before lowering it again. Isn't that pH too high?

Also, are you saying that I should ignore the "Watergram" results, which puts me outside the acceptable range when the pH is at 7.8?

Regarding my neighbors, the ones next door to me use liquid Cl only, and their pH is totally stable at about 7.4/7.5.

I feel like there has to be SOMETHING else at play here, but even after a few years of talking to people and doing research, I just can't figure it out. Is it possible that the previous owners added something to the pool -- a "clarifier" or some exotic product a pool store sold them -- that could be causing this? I would have thought that a 25% drain and refill (along with quite a few smaller drain/refills over the past 3 years), would have reduced any "odd" chemicals enough to make them irrelevant, but the pH rise hasn't changed at all. Is it possible for certain types of plaster to cause this sort of issue? The pool was plastered with a darker grey color -- is THIS a factor?

Thanks again,

Larry

 

[chem geek]

8.0 isn't too high except for three things -- one is that it can be hard to know if you're actually at 8.0 and not higher; another is that you risk metal staining if you have metal ions in the water; another is that you risk calcium carbonate scaling if the saturation index gets too high. The use of 50 ppm Borates can slow down the rate of pH rise but you weren't sure how much borates you had.

At 7.8 you'll be at +0.24 for the CSI which should be OK and unlikely to scale. At 8.0 you'll be at +0.42 which is likely still OK, but starting to get risky. We usually don't see scale form until +0.7, but your water might look more dull at that higher pH.

So if your neighbors are also using chlorinating liquid then if it's the same brand then I don't know why your pool is behaving so differently.

I don't know what could be added to the pool to have the pH rise faster. Do your neighbors use a pool cover, either a physical one or a "liquid" one? That would cut down carbon dioxide outgassing that has the pH rise. Do you have more aeration sources than your neighbor (though that doesn't explain why you now see a problem when you didn't in the past)?

New plaster rises in pH from initial curing, but older plaster if it is starting to fall apart by cracking or forming volcanoes that dribble out calcium carbonate can raise the pH as the void behind a poor plater job once opened up and exposed to the water has calcium hydroxide come out that raises both pH and CH.

 

[lalittle]

8.0 isn't too high except for three things -- one is that it can be hard to know if you're actually at 8.0 and not higher; another is that you risk metal staining if you have metal ions in the water; another is that you risk calcium carbonate scaling if the saturation index gets too high. The use of 50 ppm Borates can slow down the rate of pH rise but you weren't sure how much borates you had.

So would adding more borates be recommended, and if so, should I be careful about where my TA is when I add them?

At 7.8 you'll be at +0.24 for the CSI which should be OK and unlikely to scale. At 8.0 you'll be at +0.42 which is likely still OK, but starting to get risky. We usually don't see scale form until +0.7, but your water might look more dull at that higher pH.

Is the "CSI" something different than the "Saturation Index" number you get with the Taylor "Watergram" wheel? The wheel gives me significantly different numbers than the ones you stated. At 85 degrees F and a pH of 8.0, the Taylor Watergram gives me a +0.9 reading, which is way higher than the +0.42 you stated.

I don't know what could be added to the pool to have the pH rise faster. Do your neighbors use a pool cover, either a physical one or a "liquid" one? That would cut down carbon dioxide outgassing that has the pH rise. Do you have more aeration sources than your neighbor (though that doesn't explain why you now see a problem when you didn't in the past)?

No covers on the pool next door, physical or otherwise. I don't have any extra aeration sources, and they probably use their spa jets more than I do. I'm not sure what you mean when you say I now see a problem that I didn't see in the past. This issue (pH rise) has been happening since I first moved in. I chalked it up to new plaster for the first year or two, but now that I've been here over 3 years (and the plaster was done at least a year earlier), I don't see how that could be an issue anymore.

New plaster rises in pH from initial curing, but older plaster if it is starting to fall apart by cracking or forming volcanoes that dribble out calcium carbonate can raise the pH as the void behind a poor plater job once opened up and exposed to the water has calcium hydroxide come out that raises both pH and CH.

That sounds like a possibility, but I don't see any signs of "falling apart" or cracking. I have no way of knowing if it was a "poor" plaster job (it was done a year before I moved in), but I spoke with the previous owner and he said that they used one of the major plastering places in the area. I don't think there is any way of finding out how "good" the job was at this point, but I asked the previous owner if he could get the name of the place so I could talk to them. He said he would try to find out who did it and get back to me.

Thanks again for the feedback here,

Larry

 

[chem geek]

You can add the borates with your current TA level. Just lower the pH first before you add them. It's easiest to use boric acid as that won't change the pH much when you add it. It's slightly acidic so you can lower your pH to 7.7 then add boric acid which will lower the pH a little more closer to 7.5 (before it rises again).

The CSI is just a more accurate version of the saturation index the Watergram is trying to calculate. They just don't account for TDS. I have a Taylor Watergram and using a pH of 8.0, TA of 31 (55 minus the CYA contribution to TA), CH of 1000 and 85ºF temperature, I get a pH of saturation of 7.4 on the wheel so that would be 8.0-7.4 or +0.6 so not that far from my calculation which is more accurate. If I use 55 ppm TA on the wheel, then I get a pH of saturation of 7.15 so +0.75 as you got. So basically most of the difference was due to your not using carbonate alkalinity on the wheel -- they talk about lowering the TA you use on the wheel to account for CYA.

Sorry, I misunderstood probably mixing up threads when I thought you didn't have the problem before. Since it's always occurred, it just may be something about the plaster in your pool. And you are right that though initially new plaster makes sense for the rise, it shouldn't be happening any more.

Since your plaster is fairly new, my guess is probably wrong.

 

[lalittle]

I did another partial drain and refill, bring me to these numbers:

FC - 5.5 (at the moment)
CC - negligible
pH - 7.4 (at the moment)
TA - 70 (CYA corrected to 56.5)
CYA - 45
CH - 825

The CH didn't drop as much as I had hoped, but at least it's only 3 digits now. The CYA actually dropped a little below what I was hoping for, which concerns me since I think my pool would be considered to have the "very high amounts of sunlight" that the Pool School talks about. According to the Pool School info, even without a SWG it's normal to run CYA levels of 70 to 80 in this situation. I guess I'll wait and see what happens, but I'm wondering if I should add some CYA back in and run slightly higher Cl levels before any problems occur.

I do have a couple other concerns after the drain/refills. First, if I'm still not 100% convinced that I'm reading the CH test correctly. I just keep steadily swirling while looking for the shift from very pale pink to very pale blue as I add the last reagent. IF I'm doing it right, than 825 should be realtively accurate, but it really doesn't look like the example on the Taylor site -- it's MUCH more subtle, and I'm worried that the pink blobbies may be skewing my conclusions. I'm also worried that the TA will continue to drop due to acid additions if the pH doesn't stabilize.

Lastly, however, I'm worried that I may have opened a can of worms by doing these drain/refills. It's true that I'm really tired of having to constantly add acid (unlike all my neighbors), and that this seemed to be the only step left in my search for a solution. It's also true that my levels of both CYA and (I think) CH were way too high (my CYA was above 100), but it's ALSO true that the pool has always looked great and that I've NEVER had an algae bloom. Will the lower CYA result in a more rapid Cl percentage drop than I had before, leading to MORE work due to more frequent Cl additions? Or, will the percentage drop of Cl be about the same, allowing me to add Cl less Cl at the same intervals? Will I be living closer to the edge of problems at this point -- i.e. did I make a move away from general stability?

I can't help feeling like I may have been better off leaving good enough alone.

Larry

 

[chem geek]

You can just see your daily chlorine usage and if it's too high then increase the CYA level.

As for the pink blobbies and possible fading endpoint, try adding a good number (10 or more) of the titrating drops FIRST before adding the calcium buffer and indicator dye. Then just include that number of drops in your final count. This may help your endpoint become more distinct.

If the TA is dropping from adding acid, then that means the source of your pH rise is mostly coming from carbon dioxide outgassing. So a lower TA for your pool would be more appropriate in that case. If the acid addition wasn't lowering the TA, then that would mean the source of pH rise is from a base, such as calcium hydroxide coming from the plaster.

The lower CYA will have a higher chlorine usage, though not by that much if you get your CYA closer to 80 ppm, but again, just see where it ends up. If you didn't have algae growth before from your high CYA level (with not proportionately higher FC level) then your pool may be poor in algae nutrients making you lucky. If that is still the case, then you've already got a sort of insurance policy against algae growth if your FC gets too low for your CYA level. I don't think you moved any closer to having problems, such as algae growth. You may have moved towards greater chlorine usage, but can raise the CYA somewhat to help balance that.

 

[lalittle]

Is there any possibility that what I'm experiencing could be caused by the TA being a bit too low? I've had a number of pool people tell me that the TA should be at least 80 AFTER the CYA correction, and at the moment it's down around 55 or so. My pH goes up after adding Chlorine, goes right back down when adding acid, and I believe it rises by about 0.2ppm per day when doing absolutely nothing. EVERYBODY I talk to OTHER than the people at TFP tell me to raise the TA to 80 (after CYA correction.) I have not yet tried this, however, due to the advice of the people on the TFP forum, whose opinions I simply put a lot more stock into. That said, could I be in a situation where my TA might actually be a tad too low? Is there a possibility that raising the TA to 80 (after CYA correction) could stabilize my pH?

On that note, what would the downsides be to raising the TA a bit? Could this possibly put me in a worse situation that would be more difficult to get out of? I have yet to see anybody say that a TA of 80 (after CYA correction) could cause "problems," so would the worst case scenario to trying it be that it simply wouldn't work? Or, would this possibly just open an even bigger can of worms?

Regarding the CYA, what would the recommendation be for a good "mid point" that would keep the Cl loss from UV down to a minimum without going so high that other issues occur? I feel like the sweet spot might be around 60 or even 70, but it's troubling that the vast majority of information says to keep it at 50 or even less.

Thanks again for the help here,

Larry

 

[chem geek]

If the rise in pH is due to carbon dioxide outgassing, then raising the TA will only make that worse because TA is mostly a measure of bicarbonate in the water and the carbonates (including carbon dioxide) are how over-carbonate the water is compared to carbon dioxide in air. On the other hand, if the rise is due to a base getting added to the pool, then a higher TA will slow the rate of pH rise from that source but will not reduce the amount of acid that needs to be added. Since you are seeing the TA drop over time, then it seems that it's due to carbon dioxide outgassing and a higher TA will make that occur more quickly. You could use 50 ppm Borates as a pH buffer that doesn't increase carbon dioxide outgassing.

If you want to raise the TA, that's up to you, but it's much harder to lower the TA than to raise it.

As for CYA, 50 ppm works well for many, but in very hot sunny areas a higher CYA may be needed but not above 80 ppm.

 

[lalittle]

Since you are seeing the TA drop over time, then it seems that it's due to carbon dioxide outgassing and a higher TA will make that occur more quickly.

I'm not sure about the TA dropping over time. When I did a partial drain and refill, it rose momentarily, but it dropped to 70 (55 with CYA) pretty quickly and stabilized, and it pretty much has always hung around this level. Does this still count as the TA "dropping over time"?

You could use 50 ppm Borates as a pH buffer that doesn't increase carbon dioxide outgassing.

I'm definitely considering this, but I have some concerns about dogs -- some people say you shouldn't use borates if dogs are ever in the pool. I need to research this a bit more given that my dogs don't actually "drink" from my pool. I'm unclear if this means it's okay to use borates or not.

If you want to raise the TA, that's up to you, but it's much harder to lower the TA than to raise it.

Let's say I raise it, and it doesn't help. Would it actually cause added problems, or would it just drop down over time once again and stabilize? If it was hard to lower it again, what actual problems might that cause? I'm still real fuzzy on the downsides of giving it a try.

Thanks,

Larry

 

[Nuvene]

I'm not sure about the TA dropping over time. When I did a partial drain and refill, it rose momentarily, but it dropped to 70 (55 with CYA) pretty quickly and stabilized, and it pretty much has always hung around this level. Does this still count as the TA "dropping over time"?



I'm definitely considering this, but I have some concerns about dogs -- some people say you shouldn't use borates if dogs are ever in the pool. I need to research this a bit more given that my dogs don't actually "drink" from my pool. I'm unclear if this means it's okay to use borates or not.



Let's say I raise it, and it doesn't help. Would it actually cause added problems, or would it just drop down over time once again and stabilize? If it was hard to lower it again, what actual problems might that cause? I'm still real fuzzy on the downsides of giving it a try.

Thanks,

Larry

Lowering ph to 7.2 then aerating to raise ph will drop ta... if you haven't been dropping ph that low you may not have noticed a drop in the ta

 

[chem geek]

I'm not sure about the TA dropping over time. When I did a partial drain and refill, it rose momentarily, but it dropped to 70 (55 with CYA) pretty quickly and stabilized, and it pretty much has always hung around this level. Does this still count as the TA "dropping over time"?

I'm definitely considering this, but I have some concerns about dogs -- some people say you shouldn't use borates if dogs are ever in the pool. I need to research this a bit more given that my dogs don't actually "drink" from my pool. I'm unclear if this means it's okay to use borates or not.

Let's say I raise it, and it doesn't help. Would it actually cause added problems, or would it just drop down over time once again and stabilize? If it was hard to lower it again, what actual problems might that cause? I'm still real fuzzy on the downsides of giving it a try.

If you have evaporation and refill with water high in TA, then yes your TA may be dropping from the acid addition and getting replenished from the evaporation and refill. If you had a pool cover, then that would eliminate the evaporation and presumably you would then see your TA dropping.

As for borates and your dogs, they probably don't drink enough to be a problem, but it's definitely closer to being on the edge so best to avoid the borates if you can't train your dogs to not drink from the pool. As noted in the thread Are Borates Safe to Use?, the No Observed Adverse Effect Limit (NOAEL) is 8.8 mg/kg/day so for a 10 kg (22 pound) dog that would be 1.76 liters (7.4 cups) of water every day. The level at which first symptoms were seen was 3 times that amount.

If you raise the TA, then if you add acid to lower the pH then the TA may drop back down unless you have a lot of evaporation and refill having it stay up, but given what you have seen so far it will likely drop back down slowly over time with acid addition to control the pH.

 

[lalittle]

If you have evaporation and refill with water high in TA, then yes your TA may be dropping from the acid addition and getting replenished from the evaporation and refill. If you had a pool cover, then that would eliminate the evaporation and presumably you would then see your TA dropping.

The TA of my fill water is about 115, so it's not that high -- it's still within the recommended range of 80 to 120 ppm. What does this say about the overall picture?

If you raise the TA, then if you add acid to lower the pH then the TA may drop back down unless you have a lot of evaporation and refill having it stay up, but given what you have seen so far it will likely drop back down slowly over time with acid addition to control the pH.

My hope would be that raising the TA (since it's quite low) might buffer the pH a bit more and reduce the need for so much acid, which in turn would prevent my TA from dropping again. Is there any logic to this thinking?

As for borates and your dogs, they probably don't drink enough to be a problem, but it's definitely closer to being on the edge so best to avoid the borates if you can't train your dogs to not drink from the pool. As noted in the thread Are Borates Safe to Use?, the No Observed Adverse Effect Limit (NOAEL) is 8.8 mg/kg/day so for a 10 kg (22 pound) dog that would be 1.76 liters (7.4 cups) of water every day. The level at which first symptoms were seen was 3 times that amount.

They definitely don't intentionally drink the water. My concern is how much they might inadvertently ingest when swimming. There seem to be differing opinions on this, with some people saying that you shouldn't use borates if you have dogs, and others saying that it's not an issue unless the dogs specifically "drink" significant amounts of it. I'm just not sure what to think about this. Given any doubt, I'd have to err on the side of safety for the dogs, but borates seem like a good thing, so I'd like to use them if they don't pose any actual risk to my dogs. My dogs are rather small (22lbs and 11lbs), however, so my fear is that the risk would be higher for them.

Just to clarify, do borates pose NO risk to dogs though skin contact -- i.e. is it ONLY ingestion that's a problem? The article linked only addressed human skin as far as I can tell.

Thanks,

Larry

 

[chem geek]

So your TA in the fill water is not that high so unless you are in Arizona or other places with high evaporation due to high temperature and low humidity, then you are probably better off lowering your TA level or keeping it low.

Your logic is completely flawed thinking that a higher TA level will result in less acid usage. It is exactly the opposite because TA is a SOURCE of rising pH itself. TA represents mostly the amount of bicarbonate in the water and that is in equilibrium with carbon dioxide in the water and that outgasses to the air because pool water is over-carbonated. When the carbon dioxide outgases, it raises the pH with no change in TA. When you then add acid to lower the pH, the TA is also lowered.

If your dogs aren't using the pool as a water bowl, then they shouldn't be accidentally gulping liters-worth of water. Anyway, they are your dogs so you have to do what you think is best regarding borates. Yes, the only risk for dogs (or people or any creatures) is through ingestion, NOT through exposure to skin or through breathing the air above the pool. The reason is that the borates have virtually no skin absorption and they are not volatile. The skin absorption was not only measured against simulated human skin but done against actual albino rabbit skin and that was for concentrated boric acid. Damaged skin including that with psoriasis, eczema or urticaria (hives) can absorb boric acid much more readily. The following describes tests in dogs were the only issue was with damaged skin:

Likewise, in two dogs whose skin had been removed in the dorsolumbar area (13 × 13 cm2) or had been damaged by a third degree burn (11.5 × 11.5 cm2), occlusive application of boric acid (50 g/day for 25 days) led to a marked increase in the boric acid level in brain, liver and adipose tissue [6]. Similar findings were obtained in rabbits; quantitative differences in levels were seen when different vehicles were used [11].

Note that they had to remove the dogs exterior skin or badly burn it and apply concentrated boric acid for days. So for practical purposes, you can ignore skin absorption and focus just on ingestion.

 

[lalittle]

So your TA in the fill water is not that high so unless you are in Arizona or other places with high evaporation due to high temperature and low humidity, then you are probably better off lowering your TA level or keeping it low.

I think that I might be in one of those "other places." I may not get evaporation conditions as extreme as the hotter parts of Arizona, but I'm in Southern California where it's quite dry and gets pretty hot. How does this effect the situation? What was the "unless" referring to?

Assuming that raising the TA doesn't help, what would the result be? It seems like the higher TA would simply mean faster pH rise, which would require more acid, which in turn would drive the TA right back down again. Do I understand this correctly, or would there be other effects?

Thanks,

Larry

 

[chem geek]

According to this pan evaporation map, you probably have between 60-80" per year evaporation compared to over 100" in parts of Arizona and Texas. So while still high, it's not quite as extreme. All it means is that the TA (and CH) from the fill water that makes up for evaporation will be added to the pool. If your pool is heated, the evaporation will be higher. If it were 1/4" per day, then with an average 4.5 foot pool this is roughly 0.5 ppm TA per day increase. At 1/2" per day evaporation, it's around 1 ppm TA per day increase. Of course, if you've got pH rise and add acid to compensate, then that may keep the TA in check.

Yes, you understand the problem of higher TA correctly -- it can only hurt, not help. The only other effects of TA would be in combination with pH and CH with regard to the saturation index but it doesn't sound like you're going to let any of these parameters in combination get out of hand.