Appropriate Stabilizer Amount

[sasquatch64]

I converted from Chlorine to Salt generation last weekend. The instructions for the salt generator stated that the Cyanuric Acid (Stabilizer) should be raised to 80ppm as one of the most important steps for installation and success. When I took water to the pools store to test and told them I needed enough stabilizer to go to 80ppm they said that the amount should only be 20ppm - 50ppm and that 80ppm would cause skin itchiness and irritation.

So - I have stabilizer at 35pm and low free Chlorine (symptom of low stabilizer); but am afraid to go to 80ppm if it will cause skin irritation for the kids... who is right?

[waterbear]

I converted from Chlorine to Salt generation last weekend. The instructions for the salt generator stated that the Cyanuric Acid (Stabilizer) should be raised to 80ppm as one of the most important steps for installation and success. When I took water to the pools store to test and told them I needed enough stabilizer to go to 80ppm they said that the amount should only be 20ppm - 50ppm and that 80ppm would cause skin itchiness and irritation.

So - I have stabilizer at 35pm and low free Chlorine (symptom of low stabilizer); but am afraid to go to 80ppm if it will cause skin irritation for the kids... who is right?

Bring the CYA up to 80 ppm!

The idiot at the pool store does not know what he is talking about. The higher CYA levels will allow you to run the cell at a lower output and that will lead to less pH rise. It will have NO effect on skin irritation. (but pH spikes can). Most pool stores really do not understand how to balance water for anything besides trichlor.

(and I call the person at the pool store who told you this an idiot because I have worked with many such idiots when I worked in the retail end of the industry. They have a small amount of knowledge, misunderstand much of what they have heard, and try to come across as an 'expert'. He almost got the recommended 30 to 50 ppm for CYA for a MANUALLY CHLORINATED pool right but it was still a case of "close but no cigar" when they said 20 to 50.)

[sasquatch64]

LOL - thanks a TON! That was the direction I was leaning; but you never want itchy kid!

I appreciate the info and the fast response!

[Hope]

LOL - thanks a TON! That was the direction I was leaning; but you never want itchy kid!

I appreciate the info and the fast response!

What do you have to do to convert to using Salt?

[waterbear]

LOL - thanks a TON! That was the direction I was leaning; but you never want itchy kid!

I appreciate the info and the fast response!

What do you have to do to convert to using Salt?

Install a Salt Water chlorine generator and add salt to your pool. It is still a chlorine pool, only the chloirne is made IN the pool and does not have to be added.

[quantumchromodynamics]

Another benefit of a higher cyanuric acid level is that it will provide about an extra 10 ppm of non-carbonate alkalinity (Cyanuric acid level of 80 ppm vs. 50 ppm). Not a huge amount, but every little bit helps.

Carbonate Alkalinity can cause pH rise due to off-gassing of carbon dioxide. Non-Carbonate Alkalinity sources reduce the rate of pH rise and do not contribute to it.

[waterbear]

Another benefit of a higher cyanuric acid level is that it will provide about an extra 10 ppm of non-carbonate alkalinity (Cyanuric acid level of 80 ppm vs. 50 ppm). Not a huge amount, but every little bit helps.

Carbonate Alkalinity can cause pH rise due to off-gassing of carbon dioxide. Non-Carbonate Alkalinity sources reduce the rate of pH rise and do not contribute to it.

close but no cigar. It depends on the pH result of the Henderson-Hasselbalch equation for the buffer system. With the bicarbonate buffer system we call TA it is around 8.2. which is where the pH want to rest if the system is left alone.

It is possible for a secondary buffer system to either have a lower or higher 'setpoint' and the two buffer systems would then work in tandam or against each other.

For example, the borate buffer system, while adding to alkalinity but not carbonate alkalinity DOES make the pH want to move downward and against the bicarbonate buffer but you cannot just make a blanket statement that ANY non carbonate alkalinity will reduce the rate of pH rise.

In fact the peak buffering effect of the bicarbonate buffer occur at a pH of 6.2, far below the normal range of pool pH while the peak buffering effect of the cyanurate buffer occur at 6.8 so it is more active at the low end of normal pool pH and is more responsible for pH rise. In other words, both bicarbonate and cyanurate buffers tend to move the pH upward more than downward.

On the other hand the peak buffering of the borate/boric acid buffer system we encounter when we add borates to the water is at 9.2 and tends to move the pH downward.

I think there is a bit of misunderstanding of the bicarbonate buffer. The pH rise from CO2 outgassing is not part of the buffer. the REVERSIBLE conversion of bicarbonate into carbonic acid at lower pH and into carbonate at higher pH is the buffer. When we remove CO2 from the system we change the concentrations of the components of the buffer (and lower TA).

[quantumchromodynamics]

For example, the borate buffer system, while adding to alkalinity but not carbonate alkalinity DOES make the pH want to move downward and against the bicarbonate buffer but you cannot just make a blanket statement that ANY non carbonate alkalinity will reduce the rate of pH rise.

Once the acid and base parts of the buffer reach equilibrium at a particular pH, there should not be any pressure from the components on the pH. They merely reduce the rate of change or magnitude of change of the pH when an acid or base is introduced. They don't make the pH want to move up or down (except for the carbonate buffer due to off gassing of carbon dioxide)

Cyanuric acid has three pKas

pKa₁ = 6.88

pKa₂ = 11.4

pKa₃ = 13.5

All three are relevant in the high pH conditions inside a salt cell.

On the other hand the peak buffering of the borate/boric acid buffer system we encounter when we add borates to the water is at 9.2 and tends to move the pH downward.

Borates don't tend to move the pH down, they just resist pH rise. All forms of alkalinity (Or, more accurately Total Acidity where the pKa is within about 2.0 pH points)(carbonates, borates, phosphates and cyanurates.) reduce the rate of pH rise when a base is introduced.

I think there is a bit of misunderstanding of the bicarbonate buffer. The pH rise from CO2 outgassing is not part of the buffer.

I do understand what you are saying here. However, if pH is lowered by the addition of acid, there will be an increase in the rate of carbon dioxide out-gassing which will cause the pH to rise. Therefore, the outgassing does provide some buffering capacity.

When we remove CO2 from the system we change the concentrations of the components of the buffer (and lower TA).

The addition or removal of CO₂ does not change the TA.

I think that you are referring to carbonate alkalinity as total alkalinity. However, total alkalinity is a measure of all types of alkalinity including carbonates, phosphates, cyanurates, borates, hydroxyl ions etc.

[chem geek]

I write in this post about the effects on pH buffering of the carbonates, cyanuric acid, and borates.

There is no change in Total Alkalinity (TA) when carbon dioxide is outgassed or injected into the water and I write about that in this post including reasons why the TA may be seen to rise over time due to other factors.

[quantumchromodynamics]

Your examples are for relatively low pH compared to the pH that can occur locally inside a salt cell (where scale is most likely to form). It is my understanding that the pH can go quite high at the cathode where the hydrogen gas is generated.

At some points inside the generator, chlorine concentrations can reach 50 ppm (the normal recommended level for pool water is a maximum of 4 ppm), pH can be either close to 14 or 0 (normal levels are between 7.2 and 7.8) and temperatures can exceed 120 degrees. http://www.aquamagazine.com/articles/article.aspx?articleid=1713&zoneid=13

At any rate, I think that my original point is valid. That the additional cyanuric acid does provide some measure of additional pH buffering capacity, especially at higher pH where scale is most likely to form.

The pH buffering is helpful in the general ambient water to reduce the rate of pH rise, allowing less frequent additions of acid, and, more importantly, reducing the risk of scaling in the salt cell.

[waterbear]

I write in this post about the effects on pH buffering of the carbonates, cyanuric acid, and borates.

There is no change in Total Alkalinity (TA) when carbon dioxide is outgassed or injected into the water and I write about that in this post including reasons why the TA may be seen to rise over time due to other factors.

No, the change occurs IF the increase in CO2 is caused by the addition of acid and the CO2 ougasses so it cannot reform bicarbonate if the pH is brought back up. If you inject CO2 and it outgasses there is no net change on TA. (Although many commercial installations that use CO2 injection for pH control do see a slow upward drift to TA so in real world conditions this is not 'perfect", no matter what the cause. And I believe that it was you that pointed out in a post somewhere that escapes me at the moment that using sodium hypochorite or calcium hypochlorite as a chlorine source, which is very common in commercial installations, is the source of the additional OH- ions that are causing the rise in carbonate alkalinity in these cases.)

We have to look beyond theory and see what happens in the field to know how well something is going to work. In the field the use of CO2 for pH control is not perfect and often does lead to an increase in carbonate alkalinity (and therefore TA).

[waterbear]

For example, the borate buffer system, while adding to alkalinity but not carbonate alkalinity DOES make the pH want to move downward and against the bicarbonate buffer but you cannot just make a blanket statement that ANY non carbonate alkalinity will reduce the rate of pH rise.

Once the acid and base parts of the buffer reach equilibrium at a particular pH, there should not be any pressure from the components on the pH. They merely reduce the rate of change or magnitude of change of the pH when an acid or base is introduced. They don't make the pH want to move up or down (except for the carbonate buffer due to off gassing of carbon dioxide)

Cyanuric acid has three pKas

pKa₁ = 6.88

pKa₂ = 11.4

pKa₃ = 13.5

All three are relevant in the high pH conditions inside a salt cell.

In your previous post you said nothing about conditions inside a salt cell. At normal pool water pH the first is the most relevant.

On the other hand the peak buffering of the borate/boric acid buffer system we encounter when we add borates to the water is at 9.2 and tends to move the pH downward.

Borates don't tend to move the pH down, they just resist pH rise.

Semantics. If you have read my posts on the different forums for any period of time you would realize that I write my answers so the maximum audience has a chance of understanding them and getting something out of them. If we were discussing this in a chemistry forum it would be a different story. Richard knows this about me but we have 'compared notes' for several years now.

For example, I often refer to carbon dioxide in water and carbonic acid as the same when discussing TA even though they are not. However, for the point I am trying to get across the distinction becomes moot.

I think there is a bit of misunderstanding of the bicarbonate buffer. The pH rise from CO2 outgassing is not part of the buffer.

I do understand what you are saying here. However, if pH is lowered by the addition of acid, there will be an increase in the rate of carbon dioxide out-gassing which will cause the pH to rise. Therefore, the outgassing does provide some buffering capacity.

and at the same time removes some of the buffering capacity from the system by lowering the overall carbonate hardness.

When we remove CO2 from the system we change the concentrations of the components of the buffer (and lower TA).

The addition or removal of CO₂ does not change the TA.

If you add CO2 and then remove CO2 there is no net change on carbonate hardness but if you convert bicarbonate to CO2 by adding a source of H+ and then remove CO2 the net effect is to lower carbonate hardness and a rise in pH. Likewise, If you add CO2 and then add a source of OH- then the net effect is an increase in carbonate hardness and a rise in pH.

I think that you are referring to carbonate alkalinity as total alkalinity. However, total alkalinity is a measure of all types of alkalinity including carbonates, phosphates, cyanurates, borates, hydroxyl ions etc.

No I am not referring to carbonate alkalinity as TA but any changes in carbonate alkalinity will also change the TA. Once again I am trying not to confuse the average reader with the subtle differences between total alkalinity and carbonate alkalinity since the vast majority of the TA is carbonate alkalinity and for practical purposes they are the same.

ALSO, we have hijacked this thread far away from the OP's original question, which was how high the CYA should be for a SWG!!!!! It was quite obvious that the OP and the second poster that asked how to 'convert' to salt are newbies and

IMHO, there should have been no mention of thing that are going to be 'over there heads at this point such as:

Another benefit of a higher cyanuric acid level is that it will provide about an extra 10 ppm of non-carbonate alkalinity (Cyanuric acid level of 80 ppm vs. 50 ppm). Not a huge amount, but every little bit helps.

Carbonate Alkalinity can cause pH rise due to off-gassing of carbon dioxide. Non-Carbonate Alkalinity sources reduce the rate of pH rise and do not contribute to it.

To the OP I apologize for my part in it.