Not sure if this question was to me but I can tell you that the bench top probes should last 1-3 years depending on the frequency of use and what is being tested…..at least that is what the Apera Tech service rep told me.
Is pH 8.7 acceptable if csi is zero?
- Thread starter key1cc
- Start date
I don't really know what exactly what can happen at higher pH ranges.
There is theory and then there is real world experience.
If you want to test it out and share your results, then we will be interested to know what you find out.
This is the part that has me wondering about the inbuilt pool probes!
They test continuously
That is my dilemma. I am fine with testing and sharing to the community. I asked the question hoping I would not have to go where no man has gone before. I am willing to let my pH keep going up and keep testing to a point…… especially if I can find more insight on csi and Lsi for that matter . I need to read somewhere that scale and leaching for that matter, can’t form if you stay in the csi/Lsi range.
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Calcium carbonate solubility is based on the Ksp, which is the Molarity of the calcium ions multiplied by the Molarity of the Carbonate ions.
The Ksp for Calcium carbonate is not a single number and it varies based on different conditions and even by which source you look at.
The calcium ion molarity can be calculated from the calcium hardness reading.
The calcium hardness reading is given in ppm units of calcium carbonate equivalents.
You can convert this to calcium carbonate molarity, which is equal to the calcium ion molarity.
For example, if the calcium hardness is 250 ppm, that is 250 milligrams per liter or 0.00249783M (Moles per liter).
CaCO3 = 100.0869 g/mol.
0.00249783 X (Carbonate ion Molarity) = 3.3 x 10-9.
Carbonate ion Molarity = 0.00000132114 Moles per liter.
www.wolframalpha.com
The carbonate ion molarity can be calculated from the carbonate alkalinity and the pH.
The carbonate alkalinity reading is also given in ppm units of calcium carbonate equivalents.
You can plot the percentage of carbonate vs. the pH.
y = (100/(1+10^(10.3– x))).
For example, at a pH of 8.7, the percentage of carbonate is 2.45%.
pH.........% carbonate.
8.0...............0.49868
8.3...............0.99
8.7...............2.45
9.0...............4.77
9.5...............13.68
10...............33.386
10.3...............50
11...............83.36
11.5...............94.0649
12..................98.04
www.wolframalpha.com
So, as you can see, the pH determines how much of the bicarbonate becomes carbonate.
The carbonate concentration multiplied by the calcium ion concentration is equal to the Ksp for Calcium carbonate when the water is fully saturated.
When the carbonate concentration multiplied by the calcium ion concentration is greater than the Ksp for Calcium carbonate, the calcium carbonate will begin to come out of solution as scale and precipitate.
When the carbonate concentration multiplied by the calcium ion concentration is less than the Ksp for Calcium carbonate, the calcium carbonate should remain in solution.
The Ksp for Calcium carbonate is not a single number and it varies based on different conditions and even by which source you look at.
The calcium ion molarity can be calculated from the calcium hardness reading.
The calcium hardness reading is given in ppm units of calcium carbonate equivalents.
You can convert this to calcium carbonate molarity, which is equal to the calcium ion molarity.
For example, if the calcium hardness is 250 ppm, that is 250 milligrams per liter or 0.00249783M (Moles per liter).
CaCO3 = 100.0869 g/mol.
0.00249783 X (Carbonate ion Molarity) = 3.3 x 10-9.
Carbonate ion Molarity = 0.00000132114 Moles per liter.
250 milligrams per liter calcium carbonate to molarity - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
The carbonate ion molarity can be calculated from the carbonate alkalinity and the pH.
The carbonate alkalinity reading is also given in ppm units of calcium carbonate equivalents.
You can plot the percentage of carbonate vs. the pH.
y = (100/(1+10^(10.3– x))).
For example, at a pH of 8.7, the percentage of carbonate is 2.45%.
pH.........% carbonate.
8.0...............0.49868
8.3...............0.99
8.7...............2.45
9.0...............4.77
9.5...............13.68
10...............33.386
10.3...............50
11...............83.36
11.5...............94.0649
12..................98.04
y = (100/(1+10^(10.3– x))), x from 8 to 12 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
So, as you can see, the pH determines how much of the bicarbonate becomes carbonate.
The carbonate concentration multiplied by the calcium ion concentration is equal to the Ksp for Calcium carbonate when the water is fully saturated.
When the carbonate concentration multiplied by the calcium ion concentration is greater than the Ksp for Calcium carbonate, the calcium carbonate will begin to come out of solution as scale and precipitate.
When the carbonate concentration multiplied by the calcium ion concentration is less than the Ksp for Calcium carbonate, the calcium carbonate should remain in solution.
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For a pH of 8.7, the CSI is 0.01.
PoolMath only allows a pH entry of up to 9.0.
Over 9.0, the CSI says pH error.
You might be able to go up to a pH of 9.0, but I really do not know what type of issues might happen because no one really has any experience with trying to maintain a pH that high.
I would keep the pH below 8.0.
If you want to experiment and go above 8.0, keep good records and let us know what you find out.
PoolMath only allows a pH entry of up to 9.0.
Over 9.0, the CSI says pH error.
You might be able to go up to a pH of 9.0, but I really do not know what type of issues might happen because no one really has any experience with trying to maintain a pH that high.
I would keep the pH below 8.0.
If you want to experiment and go above 8.0, keep good records and let us know what you find out.
So what you are saying (with your supporting data) is that as long as pH is under 9 and the CSI conditions are within the desired range of -0.3 to +0.3.....then calcium carbonate should not precipitate and consequently should not form scale? If that is the case, why do you conclude with "I would keep the pH below 8"....
since calcium carbonate scale formation is directly related to it solubility product range, shouldn't that dictate when scale forms rather than an arbitrary pH of 8 or 8.2 or 8.x.........? And if that's the case, isn't that what the csi is for? Which brings me back to my original inquiry of can I use csi to manage my pool water (without pH limitations). I believe your answer is yes if pH is less than 9 and unknown if pH is over 9?
since calcium carbonate scale formation is directly related to it solubility product range, shouldn't that dictate when scale forms rather than an arbitrary pH of 8 or 8.2 or 8.x.........? And if that's the case, isn't that what the csi is for? Which brings me back to my original inquiry of can I use csi to manage my pool water (without pH limitations). I believe your answer is yes if pH is less than 9 and unknown if pH is over 9?
Algae bloom while getting CYA down to manageable levels
You can read my initial post regarding my pool situation here; http://www.troublefreepool.com/finally-took-possesion-of-new-house-and-cya-is-over-140-t24944.html To make a long story short (thank god I am on holidays to handle this) I had an excellent opportunity to drain and refill the pool...
www.troublefreepool.com
pH is an item that you’d want to keep some control over rather than letting it run wild otherwise you’d start to open other cans of worms.
Algae bloom while getting CYA down to manageable levels
You can read my initial post regarding my pool situation here; http://www.troublefreepool.com/finally-took-possesion-of-new-house-and-cya-is-over-140-t24944.html To make a long story short (thank god I am on holidays to handle this) I had an excellent opportunity to drain and refill the pool...
pH is an item that you’d want to keep some control over rather than letting it run wild otherwise you’d start to open other cans of worms
With the pool water is in the low 40’s approaching the 30’s I am not to concerned about algae. But you bring up a good point along the lines of….. pools without cya stabilization since they require lower pH for the chlorine to be effective…but pools that are stabilized with cya like mine …. A related question would have to be is the cya to chlorine relationship still viable if the pH approaches 9? That question I personally am not really interested in because during the warm water swimming season I would not let-the pH get anywhere close to 9.
My current interest is about new plaster Pool Balance in the winter to prevent some of the issues I read about (scale and leeching) rather than about Sanitization at this time.
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Awesome as I suspect THIS is what many of us would be mostly concerned about, somebody with warm water playing around trying to totally ignore pH all year long.….even with warm water.
You have a pretty good understanding of the basics.
As far as I know, you should not get scale if the CSI is below 0.0.
However, there are different types of calcium carbonate and also different types of calcium scale like calcium sulfate, calcium phosphate etc.
If you look up the ksp of different types of calcium carbonate, you will find different values for each type as well as different value for different conditions like water temperature, salinity etc.
My recommendation to stay below 8.0 is conservative due to the many unknowns involved.
Without having any experience maintaining a pool at a pH over 8.0 for a long period of time, I cannot say if there are risks that can happen that are not accounted for in the CSI.
www.nature.com
en.wikipedia.org
en.wikipedia.org
en.wikipedia.org
As far as I know, you should not get scale if the CSI is below 0.0.
However, there are different types of calcium carbonate and also different types of calcium scale like calcium sulfate, calcium phosphate etc.
If you look up the ksp of different types of calcium carbonate, you will find different values for each type as well as different value for different conditions like water temperature, salinity etc.
My recommendation to stay below 8.0 is conservative due to the many unknowns involved.
Without having any experience maintaining a pool at a pH over 8.0 for a long period of time, I cannot say if there are risks that can happen that are not accounted for in the CSI.
Variations in the Crystalline Form of Calcium Carbonate precipitated from Artificial Sea Water - Nature
CALCIUM carbonate can exist in three polymorphic forms, which in the order of their usual stabilities are calcite, aragonite and vaterite. Calcite is the most stable and the least soluble, and, therefore, the form in which calcium carbonate would be expected to precipitate from sea-water. It has...
www.nature.com
Aragonite - Wikipedia
Vaterite - Wikipedia
Calcite - Wikipedia
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PoolMath was designed to work well in the pH range of about 7.0 to 7.9.
You really need to do the calculations for all chemistry above about 8.3 and not rely on PoolMath.
You need to calculate the effects of things like phosphates, borates, cyanurates etc.
These all change based on the pH.
The main types of calcium scale are calcium carbonate, calcium phosphate, calcium silicate and calcium sulfate.
The Case of the Mysterious Pool Deposits
The Mystery of the Pointed Crystals
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%.
Borate C.F (correction factor) based on pH.
pH.......CF
7.2.....0.051
7.4.......0.0786
7.6......0.1248
7.8......0.1989
Cyanuric Acid correction factor based on pH.
pH........CF
7.0.......0.22
7.1.......0.24
7.2.......0.26
7.3.......0.28
7.4.......0.30
7.5.......0.32
7.6.......0.33
7.7.......0.34
7.8.......0.35
7.9.......0.36
For example, if the pH = 7.6, TA = 90, Borate = 50 and CYA = 70, the adjusted alkalinity is 90 - (70 x 0.33) – (50 x 0.1248) = 60.66.
At the end of the day, it is your choice where to run the pH based on whatever you feel good about.
My recommendation is to not exceed 8.3, but you can do whatever you want.
You really need to do the calculations for all chemistry above about 8.3 and not rely on PoolMath.
You need to calculate the effects of things like phosphates, borates, cyanurates etc.
These all change based on the pH.
The main types of calcium scale are calcium carbonate, calcium phosphate, calcium silicate and calcium sulfate.
The Case of the Mysterious Pool Deposits
The Mystery of the Pointed Crystals
Borates buffering pH rise.
1÷(1+10^(pKa – pH)) = borate percentage.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%.
Borates and Adjusted Alkalinity[edit]
Adjusted TA = TA – (CYA X CYA C.F) – (Borate x Borate CF)Borate C.F (correction factor) based on pH.
pH.......CF
7.2.....0.051
7.4.......0.0786
7.6......0.1248
7.8......0.1989
Cyanuric Acid correction factor based on pH.
pH........CF
7.0.......0.22
7.1.......0.24
7.2.......0.26
7.3.......0.28
7.4.......0.30
7.5.......0.32
7.6.......0.33
7.7.......0.34
7.8.......0.35
7.9.......0.36
For example, if the pH = 7.6, TA = 90, Borate = 50 and CYA = 70, the adjusted alkalinity is 90 - (70 x 0.33) – (50 x 0.1248) = 60.66.
At the end of the day, it is your choice where to run the pH based on whatever you feel good about.
My recommendation is to not exceed 8.3, but you can do whatever you want.
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The equilibrium changes based on the pH.
You also get mostly hypochlorite vs. hypochlorous acid.
Hypochlorous acid is the more effective form of chlorine, so the chlorine is not as effective.
You ask good questions, but no one really has any experience running a pool at a pH over 7.9.
Theory is great, but it only goes so far as there are always unknown factors that theory does not address until you get enough observational data.
You should calculate the saturation of all types of scale if you go above a pH of 8.3.
Calcium phosphate is Formula: Ca3(PO4)2.
At 25°C and pH 7.00, Ksp for calcium phosphate is 2.07 × 10−33
phosphoric acid (H3PO4) has 3 pKa values. 2.1, 7.2 and 12.3.
So, even though phosphoric acid has a high pKa for the phosphate ion, the Ksp of calcium phosphate is very low and the risk of calcium phosphate scale is high with very low levels of phosphate.
You need to calculate the actual carbonate concentration by subtracting the contributions of things like phosphate, cyanurate and borate to the total alkalinity.
____________________________________________________________________________________
Cyanuric acid vs Cyanurate.
____________________________________________________________________________________
Boric acid vs. borate.
____________________________________________________________________________________
Bicarbonate vs. carbonate.
____________________________________________________________________________________
Hypochlorous acid vs. hypochlorite.
____________________________________________________________________________________
H2PO4- vs. HPO42-
____________________________________________________________________________________
HPO42- vs. PO43-
____________________________________________________________________________________
www.wolframalpha.com
www.wolframalpha.com
Calcium phosphate is Formula: Ca3(PO4)2.
At 25°C and pH 7.00, Ksp for calcium phosphate is 2.07 × 10−33
phosphoric acid (H3PO4) has 3 pKa values. 2.1, 7.2 and 12.3.
So, even though phosphoric acid has a high pKa for the phosphate ion, the Ksp of calcium phosphate is very low and the risk of calcium phosphate scale is high with very low levels of phosphate.
You need to calculate the actual carbonate concentration by subtracting the contributions of things like phosphate, cyanurate and borate to the total alkalinity.
____________________________________________________________________________________
Cyanuric acid vs Cyanurate.
____________________________________________________________________________________
Boric acid vs. borate.
____________________________________________________________________________________
Bicarbonate vs. carbonate.
____________________________________________________________________________________
Hypochlorous acid vs. hypochlorite.
____________________________________________________________________________________
H2PO4- vs. HPO42-
____________________________________________________________________________________
HPO42- vs. PO43-
____________________________________________________________________________________
plot y = 100÷(1+10^(7.53 – x)) and y = 100-(100÷(1+10^(7.53 – x))), x from 5 to 10 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
plot y = 100÷(1+10^(10.3 – x)) and y = 100-(100÷(1+10^(10.3 – x))), x from 8 to 12 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
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Thank you for participating in this exploratory exercise of mine. You have helped me expand my understanding of pool chemistry.
One of my bottom-line takeaways of this exercise is that there is at least a comfort level with using csi as a vehicle for pool balance up to pH 8.3.... but beyond that, it is risky because it has yet to be sufficiently explored.
- May 3, 2007
- 16,930
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
From my own experience, scale is still a possibility with a negative CSI for both the tile line and for an SWG. I believe this is because at the tile line, the local conditions are different than in the main body of water primarily due to evaporation and CO2 outgassing near the surface. Also, for SWGs, the PH at the plate boundary can be higher than the main body of water so my SWG still gets some scale even at CSI levels of -0.3.
The tile line also gets water that evaporates and leaves behind calcium scale.
The water is constantly wetting the tile just above the water line due to wind action and other movement and as the water dries, the solids are left behind.
The scale is every type of scale possible because, as the water dries, all scale will precipitate as the concentrations reach saturation levels.
This is why tile scale tends to be the worst to remove.
The scale will include calcium carbonate, calcium phosphate, calcium sulfate, calcium silicate, sodium chloride, calcium chloride, magnesium carbonate and various types of mixed compounds.
The water is constantly wetting the tile just above the water line due to wind action and other movement and as the water dries, the solids are left behind.
The scale is every type of scale possible because, as the water dries, all scale will precipitate as the concentrations reach saturation levels.
This is why tile scale tends to be the worst to remove.
The scale will include calcium carbonate, calcium phosphate, calcium sulfate, calcium silicate, sodium chloride, calcium chloride, magnesium carbonate and various types of mixed compounds.
You can also get scale in a heater heat exchanger due to higher temperatures even if the water in the pool has a - 0.3 CSI.
- May 3, 2007
- 16,930
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
All of these reasons are why I actually have targeted -0.6 CSI when my pool water is at a higher CH (>400 ppm). I just refilled the pool and it is now at 125 ppm so I may try a lower CSI once again and see how things go.