PH 8.0 - OK if CSI Good?

[TexEdmond]

83 today, have had tons of rain.

which is a whole-pool aerating event. No wonder your pH went up so quickly in a day.

For what it's worth, I'm dropping 20oz MA per day into my 70-80ppm TA pool. 16oz every third day isn't so terrible, I was used to doing 60 - 80 oz and playing the yo-yo game trying to get my TA down.

CYA only buffers your pH from dropping - not rising so I'm thinking this has no effect on my pH issue.

I don't think this is correct? Maybe a typo? CYA primarily helps keep your FC from falling and adding it will slightly drop pH.

 

[RPSalty]

TLDR: pH rises from 7.2 to 8.0 in 60 hours, but @JoyfulNoise said he is able to go 10-14 days without adding acid due to proper TA and Borates. I'm wondering if I should lower my TA a bit, increase my CYA a bit, and add borates?

Hey all, so appreciate your help both directly and indirectly through just reading through the forums. My pool really has been trouble free in terms of chemicals and I can't understate how satisfying it is to have simply never had algae, never had eye or skin discomfort - TFP has made it a very simple series of concepts that are remarkably predictable.

However, the pH is just going up way too fast for my preference. On Thursday at about 7pm, I tested pH at 8.0 and put in the suggested amount of muriatic acid to bring it to 7.2 (I know that's low, wanted to see how it would affect the rise). I tested at 7.2 two hours later at 9:30pm. Just 12 hours later, the pH rose to 7.4 (Friday at 9:30am). I did not test the water yesterday but this morning at around 9:30 the pH was 8.0 again.

I generally test my water 2 or 3 times per week and my pH is ALWAYS high so I'm ALWAYS adding around 16oz to bring it from 8 or 8.2 to 7.4 nearly twice a week because I know in 3 days it will be right back up. While this isn't an awful terrible thing, I'm hoping there's a way to slow down this process so I can adjust only once or twice a week and end up in that 7.6-7.8 range during that time.

RELEVANT POOL DETAILS:
• Filled 04/23 - plaster pebble finish
• 12,500 gallons
• 1 bubbler on a 3hp intelliflo that I keep on 600 RPM 24/7 split in half with a bypass valve so it just barely breaks the surface of the water
• 1 5ft sheer descent that I never turn on because it's messed up and is being replaced
• 1 5ft spa spillover that only trickles over the side with hardly any bubbles visible at the 1700 and 2100 RPM settings I run it at. I only run it for a few hours sometimes on the weekends

TAYLOR 2006C TODAY:
PH - 8.0
TA - 70
CYA - 50ish (I can see that stupid dot no matter what, but based on pool store testing I think I'm getting the hang of what it should look like)
FC - 12.2 (getting pump speeds and timing dialed in and accidentally bumped this up too high)
CC - 0.0
CH - 340
SALT - 3000
TEMP - 86

I logged on today to search for answers now that I have more data (in my mind) about my constant PH rise. I read through this post and don't see anyone address how long you are running your SWG per day. Time of sunshine exposure is a consideration. My pool is roughly your size, no screen enclosure and just north of Tampa. SWG runs at 20%, 10 hours a day, 0800-1800. That equates to the SWG running for 2 hours a day. SWG's are either on or off. The pool doesn't see the sun until roughly noon (tall trees to the East). The size of my SWG is for a 35K pool and is partly why it runs so little. Overcast days, chlorine loss is reduced, but the SWG still runs and produces not only chlorine, but rising PH.

When my CYA was too low I couldn't keep the chlorine level up, so I ran the SWG longer. I got the chlorine I needed and a lot more PH. When I got my CYA to my goal of 80, I was able to reduce the SWG %, keep the FC roughly 5.0, and slow but not eliminate PH rise.

I read further in this thread, your chemistry is leveling out so this may be moot, but something to consider.

 

[JamesW]

However, if I understand it right after the video, similar to TA, CYA only buffers your pH from dropping - not rising so I'm thinking this has no effect on my pH issue.

I don't think this is correct? Maybe a typo? CYA primarily helps keep your FC from falling and adding it will slightly drop pH.

Depending on the pH, part of the CYA is in the form of cyanuric acid and part is in the form of cyanurate.

The cyanuric acid contributes to the “Total Acidity” of the water, which buffers pH rise from introduced bases.

The cyanurate contributes to the “Total Alkalinity”, which buffers the pH from pH drop from introduced acids.

pH......CYA %.....Cyanurate %

7.2.......32...............68

7.4.......23..............77

7.6.......16..............84

7.8......11..............89

8.0........7..............93

C₃H₃N₃O₃ is cyanuric acid.

C₃H₂N₃O₃ is cyanurate.

When a base is added, some of the hydrogen ions are released from the cyanuric acid and that partially neutralizes the base. This converts some of the cyanuric acid into cyanurate.

When an acid is added, some of the hydrogen ions from the acid get connected to the cyanurate and that reduces the effect that the acid would have had on the pH. This converts some of the cyanurate to cyanuric acid.

So, CYA buffers from pH rise and pH drop.

Total Alkalinity from all sources buffers the pH drop caused by added acids.

The problem with carbonate alkalinity is that it causes pH rise due to the carbon dioxide created from the carbonic acid.

As the carbon dioxide is lost, the pH will rise.

Cyanurate alkalinity does not cause pH rise.

 

[JamesW]

the SWG still runs and produces not only chlorine, but rising PH.

The SWG is pH neutral as long as the amount of FC created is equal to the amount lost.

In the long run, SWGs are pH neutral.

Any rising pH is from the carbonate alkalinity and carbon dioxide being lost..

 

[TexEdmond]

Thank you, James. I know I am progressing in my TFP education when I can read that and not just go completely cross-eyed. Probably another discussion for a "deep end" forum, but that's really fascinating. It would seem that there'd be some sort of curve to answer "How much?" the CYA buffering affects the overall pH change when adding acid? It'd seem a very high carbonate / low CYA pool would behave differently than a low carbonate / low CYA pool.

There seems to be some disagreement here among people who are very knowledgeable on whether SWGs contribute to pH change due to hydrogen bubbling.

 

[JamesW]

It would seem that there'd be some sort of curve to answer "How much?" the CYA buffering affects the overall pH change when adding acid?

PoolMath tells you the effect on pH from adding acid.

The TA and borate determine the effect on pH from acid additions.

The cyanurate is included in the TA number.

As you can see here, the borate doubles the amount of acid needed to move the pH from 7.9 to 7.2.



1÷(1+10^(9.15 – pH)) X 100 = borate percentage.

pH.....Borate.....Boric Acid.

7.2.....1.1%..........98.9%

7.4.....1.7%..........98.3%

7.6.....2.7%..........97.3%

7.8.....4.3...........95.7%

8.0.....6.6...........93.4%.

 

[JamesW]

There seems to be some disagreement here among people who are very knowledgeable on whether SWGs contribute to pH change due to hydrogen bubbling.

There are many people who experience no pH rise.

If pH rise was a fundamental effect of SWG operation, you would not have many examples of people reporting no pH rise.

For example, if you add 1 lb of sodium hydroxide to your pool every day, the pH will rise unless there is something offsetting the rise.

If you had 1,000 people adding 1 lb of sodium hydroxide per 10,000 gallons to their pool every day, virtually 100% of the people will report continuous pH rise because it is a fundamental effect of adding sodium hydroxide.

If you have many reports of zero, or near zero, pH rise while using a SWG, then it can’t be a fundamental effect especially when the reports are for situations where the pH would rise if the effect was real and fundamental.

SWGs are pH neutral.

All pH rise is due to carbon dioxide offgassing or other reasons like maybe new plaster releasing calcium hydroxide or mature plaster releasing calcium carbonate due to low CSI.

 

[TexEdmond]

The cyanurate is included in the TA number.

I think that really makes sense and brings it home for me... Do I have this correct? If I add acid to my pool, it does an "equal opportunity" conversion on carbonate and cyanurate into Carbonic(?) and Cyanuric acids. That carbonic acid then off-gasses CO2 just like a soda, and the pH rises. But the CYA doesn't off-gas, and as the pH rises, it slowly releases itself back into cyanurate? I still need to understand borates better, but I did notice the increase in acid demand for the same pH change.

That also makes total sense about SWG being pH neutral. My question about the SWG was maybe better asked, "Is the disagreement just a misunderstanding on my part, or does the gas creation (even if it's just hydrogen) in the SWG cell create more surface area / mechanical action that could speed up that natural carbonic acid / CO2 offgassing? To that end, could it be said that SWGs can speed that pH rise process with their normal function that doesn't itself change the pH?"

 

[JamesW]

If I add acid to my pool, it does an "equal opportunity" conversion on carbonate and cyanurate into Carbonic(?) and Cyanuric acids.

Each is affected differently because their pKa values are different.

Carbonic acid pKa = 6.37.

Cyanuric acid pKa = 6.88

Boric acid pKa = 9.2

The pKa of carbonic acid and cyanuric acid are close enough that they can be combined.

Technically, they should be done separately for maximum accuracy.

The pKa of boric acid is far enough away from the other two values that it has to be calculated separately.

That carbonic acid then off-gasses CO2 just like a soda, and the pH rises.

Yes.

But the CYA doesn't off-gas, and as the pH rises, it slowly releases itself back into cyanurate?

Yes.

My question about the SWG was maybe better asked, "Is the disagreement just a misunderstanding on my part, or does the gas creation (even if it's just hydrogen) in the SWG cell create more surface area / mechanical action that could speed up that natural carbonic acid / CO2 offgassing?

Any sort of agitation can increase CO2 offgassing.
However, the CO2 can mostly redissolve back into the water before it has a chance to offgass.

To that end, could it be said that SWGs can speed that pH rise process with their normal function that doesn't itself change the pH?"

Correct.

 

[JamesW]

Also, the whole notion of needing a TA buffer for pH is “mostly” nonsense.

pH does not need a buffer to protect against pH drop because no one is just randomly adding acid to pools.

If you had vandals coming by on a regular basis and adding a gallon of acid to your pool, then maybe a TA buffer would be helpful.

As long as no one is adding anything to the pool to move the pH up or down, there really is no need to have any sort of buffer.

This is for SWG or liquid chlorine pools.

Trichlor pools add acid from the tabs, so they need TA to buffer pH drop and to recover from pH drop by way of carbon dioxide offgassing.

The pH does not just start “bouncing” around with a low TA.

Distilled water has no TA and the pH sits happily at 7.0 forever.

The only buffer that really helps is the total acidity of boric acid to buffer pH rise in the cell at the plates where the hydrogen is created.

Hydroxide is produced in the cell.

2H2O --> H2 + 2OH-

2 water –> Hydrogen gas + 2 hydroxide.

The hydroxide converts bicarbonate to carbonate.

HCO3- + OH- --> H2O + CO3^2-

Bicarbonate + hydroxide --> water + carbonate.

Then, the carbonate connects to calcium and you get calcium carbonate.

Ca^2+ + CO3^2- --> CaCO3

Calcium + carbonate --> calcium carbonate.

Boric acid protects from pH rise by accepting and binding to the hydroxides produced in the cell due to the production of hydrogen.

B(OH)3 + OH- --> B(OH)4-

Boric acid + hydroxide --> Borate.

So, it's really boric acid and total acidity that provides the protection from pH rise and cell scaling.

The main reason for TA is to provide carbonate for pools with plaster so that the CSI can be managed.

Other than that, TA is mostly unnecessary and counterproductive for SWG or liquid chlorine pools.

 

[TexEdmond]

I hadn't once thought about looking at what happens in a SWCG by deliberately not looking at chlorine ions. Thanks for explaining the pKa, I never got far enough to know that term, but it makes sense. It's been a long time since chemistry. Is it safe for me to look at borate ion having a -3 charge and understand that's why it's so thirsty for hydrogen ions and it takes roughly double the amount of acid to drop pH when borates are present? Carbonates, only having a -1 charge have less pull?

Edit: re-reading about SCG and borates, it makes sense that it'd be similarly inclined toward hydroxide ions in the other direction.

 

[TexEdmond]

If you had vandals coming by on a regular basis and adding a gallon of acid to your pool

One man's vandal is another's savior... Depends on the TA of the fill water, yes?

 

[Newdude]

The SWG PH debate will probably outlive us all, but IMHO, the increased pump runtime and subsequent return jets aerating get overlooked as the root cause more often than not.

 

[RPSalty]

There are many people who experience no pH rise.

If pH rise was a fundamental effect of SWG operation, you would not have many examples of people reporting no pH rise.

For example, if you add 1 lb of sodium hydroxide to your pool every day, the pH will rise unless there is something offsetting the rise.

If you had 1,000 people adding 1 lb of sodium hydroxide per 10,000 gallons to their pool every day, virtually 100% of the people will report continuous pH rise because it is a fundamental effect of adding sodium hydroxide.

If you have many reports of zero, or near zero, pH rise while using a SWG, then it can’t be a fundamental effect especially when the reports are for situations where the pH would rise if the effect was real and fundamental.

SWGs are pH neutral.

All pH rise is due to carbon dioxide offgassing or other reasons like maybe new plaster releasing calcium hydroxide or mature plaster releasing calcium carbonate due to low CSI.

I have been adding on average 6oz MA daily to stay around 7.6. Based on the statement above, my mature plaster is a factor that is causing my PH to rise. The CSI avg is -0.05 for this year. Before I got the CYA and FC managed, FC reached 12.0. My solution was to turn off the SWG. It was off for three days and I did not need to add as much MA for those three days. I have a spa spillover that I attributed to the continued but slow rise in PH.
Since I've followed and supported TFP my pool has never looked or felt better. I am happy the only chemical I add regularly is MA. I add salt and cyanuric acid as needed. But is 6oz MA daily too much? I am striving to be one of those people with no PH rise.

 

[JamesW]

When lowering the pH from 8.0 to 7.2, the percentage of borate goes from 6.6% to 1.1%.

So, the buffering depends on how much borate needs to be converted into boric acid.

pH.....Borate.....Boric Acid.

7.2.....1.1%..........98.9%

7.4.....1.7%..........98.3%

7.6.....2.7%..........97.3%

7.8.....4.3...........95.7%

8.0.....6.6...........93.4%.

B(OH)₄^- + H⁺ --> B(OH)₃ + H₂O.

Every mole of borate that has to be converted from borate to boric acid requires 1 mole of hydrogen ions.

50 ppm boron in 100,000 liters is 5,000 grams of boron.

5,000 grams of boron is 462.4919 moles of boron or borate.

6.6% of 462.4919 is 30.52 moles.

1.1% of 462.4919 is 5.0874 moles.

So, we need to convert 25.43 moles of borate to boric acid, which will take 25.43 moles of hydrochloric acid.

25.43 moles of hydrogen chloride is 927.27 grams of hydrogen chloride.

20 baume contains 370.88 g HCl/liter.

927.27 kg/370.88 kg = 2.500 liters of HCl.

4.873 liters - 2.186 liters = 2.687 liters of 31.45% acid needed to convert the borate to boric acid.
__________________________________________________________________________________________________________

Total Acidity is the same type of concept of a buffer but in reverse.

For example, to change the pH from 7.2 to 8.0 with sodium hydroxide, we need to convert 25.43 moles of boric acid to borate, which will take 25.43 moles of sodium hydroxide, which is 1,017 grams of sodium hydroxide.




C₃H₂N₃O₃ + H⁺ --> C₃H₃N₃O₃

Every mole of cyanurate that has to be converted from cyanurate to cyanuric acid requires 1 mole of hydrogen ions.

50 ppm cyanuric acid in 100,000 liters is 5,000 grams of cyanuric acid.

5,000 grams of cyanuric acid is 38.74 moles of cyanuric acid.

The cyanurate percentage goes from 93 to 68%, which is 25%

25% of 38.74 moles is 9.685 moles.

So, we need to convert 9.685 moles of cyanurate to cyanuric acid, which will take 9.685 moles of hydrochloric acid.

9.685 moles of hydrogen chloride is 353.12 grams of hydrogen chloride.

20 baume contains 370.88 g HCl/liter.

353.12 g/370.88 g = 0.952 liters of HCl.

So, it takes 0.952 liters of 31.45% hydrochloric acid to convert the cyanurate to cyanuric acid.

You can do the same calculation for the carbonate and bicarbonate to see the amount of acid needed for that buffer.

The remaining amount of acid goes towards actually lowering the pH.

As you can see, the buffers really absorb a lot of the acid and the amount of acid that actually changes the pH is very small.

 

[JamesW]

I have been adding on average 6oz MA daily to stay around 7.6.

A pH of 7.8 is more stable.

As long as the CSI does not go above +0.1, then I would allow the pH to remain at 7.8 without taking any action.

 

[TexEdmond]

But is 6oz MA daily too much? I am striving to be one of those people with no PH rise.

I don't know. I've yanked my TA down as low as I could get it to go, and the last time I dropped pH to 7.0-7.2 and aerated back up, it just stayed at 70. I'm either doing the test wrong, my reagents are incorrect, my sprinklers insta-aerate enough 230TA well water back in daily, or something else is off. I'm averaging 20oz of 20 Baume per day for the last few days just to keep CSI. That might just be as good as it gets, and the wife and I discussed installing an IntellipH the other day to just keep it as automated as possible.

Do you know your fill water TA numbers? I notice you're on well water with auto-fill... it might be sneaking your TA back up without noticing?

 

[RPSalty]

So adding and testing for borates is a way to decrease PH rise. Would I want to add another regime or continue with 6oz MA a day?

I was going to start another thread... This week I am allowing the PH to stay higher =>7.8 and I noticed PH doesn't rise as fast. Went two days and then only had to add 4oz MA. Does PH reach a point that it doesn't rise anymore?

With that in mind, I use the Taylor K-1000 to test chlorine and PH daily. The chlorine side always shows off the scale, but the weekly FC drop test shows 5.0. Is it possible the PH side is also off and reading higher than the PH really is? So that by adding all the MA I've actually been keeping the PH too low? I don't use another method to test PH.

 

[TexEdmond]

Does PH reach a point that it doesn't rise anymore?

It's my understanding that if you don't have any crazy TA situation with fill water, and you're not adding Cal-Hypo or other chems that increase carbonate / TA, the pH and TA numbers eventually balance and things sit still. You sound like you're pretty close, honestly, but I'm not the expert.

Borates sound like they'll mean you'll have to add more total acid, just less frequently, but it'd basically average out. They are definitely recommended for SWG cell longevity.

The chlorine side always shows off the scale, but the weekly FC drop test shows 5.0. Is it possible the PH side is also off and reading higher than the PH really is? So that by adding all the MA I've actually been keeping the PH too low? I don't use another method to test PH.

This is why the TFP recommended FC test is the DPD powder test. It'll give accurate results up to very high FC levels and not just be the 5ppm comparator block. Basically nobody uses that drop test here except maybe to check if levels have fallen dangerously low. Any FC above 10ppm will throw off the pH comparator test on the high side, so you may be right. Other options are a well-calibrated electronic pH meter, but it's really not necessary to keep FC at 10ppm or higher unless you've got some crazy CYA levels.

 

[RPSalty]

Sorry, my weekly test is the DPD powder and the R-0871 drops. My daily comparator block is what is off the scale, so that makes me wonder if the pH comparator is off as well. My FC is 5.0 by the DPD test. I'm not too confident in my electronic pH meter, reads something different testing the same distilled water sample 10 minutes apart.

Do you know your fill water TA numbers? I notice you're on well water with auto-fill... it might be sneaking your TA back up without noticing?

My well water TA is 230. My pool TA is 70 and of late has been stable.