CYA not considered in Pool Math?

[DougJack]

As I understand it, if there is sufficient CYA in the hot tub, as much as 20X calculated Cl needs to be added as pool math calculates. This is because the approximate equilibrium point of CYA bound FC is about 95% of the total FC.

To some degree, this is as much a question as a statement - I'm not a chemist.

 

[Bperry]

As I understand it, if there is sufficient CYA in the hot tub, as much as 20X calculated Cl needs to be added as pool math calculates. This is because the approximate equilibrium point of CYA bound FC is about 95% of the total FC.

To some degree, this is as much a question as a statement - I'm not a chemist.

Poolmath considers CYA most definitely. Can you explain what you mean?

 

[Newdude]

Can you explain what you mean?

Doug is asking if his statement is correct, so it's both a statement and a question.

Depending on how deep you want to go Doug, you got the gist of it. More CYA = the need for more FC, which poolmath does recognize by suggesting higher targets.

Its spelled out here without going too deep.

CYA Chlorine Relationship - Further Reading

Go buck wild down the rabbit hole if desired.

Pool Chemistry - Further Reading

www.troublefreepool.com

 

[AUSpool]

As I understand it, if there is sufficient CYA in the hot tub, as much as 20X calculated Cl needs to be added as pool math calculates. This is because the approximate equilibrium point of CYA bound FC is about 95% of the total FC.

To some degree, this is as much a question as a statement - I'm not a chemist.

PoolMath doesn’t automatically set a ideal FC/CyA ratio, that’s for each user to decide using the
FC/CYA Levels as a tool to do this.

20X is a number that has been put out there in some recent literature to set a maximum CyA level from a desired FC target as a starting point. But this is targeted at commercial operations not the domestic back yard pool or tub. 20X the calculated FC would be well above
SLAM Process levels and way more then is needed but I may not be understanding the question correctly.

It’s more accurate to say that FC is bound to CyA although that’s not exactly true either. The entire process is very complicated and understanding the process doesn’t lead to ideal ratio, there is still more to it like kill rates and compromise for ideal bather comfort.

There are 10 equilibrium reactions plus the hypochlorous acid / and hypochlorite ion equilibrium that are constantly in flux but maintaining equilibrium.

95% is close, l think it’s closer to 97% but depends on the equilibrium. It sounds like the active form of FC is limited but if an ideal ratio is maintained there is still more than enough to ensure safe kill rates of pathogens and the required oxidation.

As the active form of FC (HOCl) is used equilibrium is maintained and more HOCl is released from the CyA/H2Cy complex. The ratio will drop a little as it’s used but it’s up to use to maintain that.

7.5% FC of the CyA value is often given as the minimum ratio but I like to run at 10% or a little more, it’s a nice easy % to work with.

 

[AUSpool]

As I understand it, if there is sufficient CYA in the hot tub, as much as 20X calculated Cl needs to be added as pool math calculates.

Simple answer from how I’m reading that is no.

Let’s say the CyA is at 30ppm and my target FC is 3ppm (10%). If I’m at 1ppm FC from testing PoolMath tells me to add 166ml in 10kL to get me back to 3ppm FC 20X that would be 3,320ml which would bring my FC up to 41ppm, crazy high.

This is because the approximate equilibrium point of CYA bound FC is about 95% of the total FC.

Attempting to raise that 5% back to 100% by adding 20X the amount of FC is the same as not using any CyA and running at 1-3ppm with no CyA which kind of defeats the purpose and benefits of using CyA. We want to maintain that 95% chlorinated cyanurates to active free chlorine by maintaining our selected FC/CyA ratio.

 

[DougJack]

Hi, thanks for the responses - sorry I didn't get back quickly, but I'm traveling. I understand that this can be a complicated area. I'm trying to simplify things for myself, but hopefully not oversimplify! The first thing I'm trying to understand is if Pool Math considers CYA when recommending dosing level. For example: FC = 1; CYA = 0. Target = 3; recommendation (liquid chlorine @12.5%) = 25 ml. If I change Target to 5 the recommendation doubles to 50. If I change FC to 2 the target = 12. Both linearly proportional. If I change CYA to 30 there is no change to either recommendation. That response is one of the 2 reasons why I asked my question. I'll leave the other question for later. Maybe I'm not using Pool Math correctly.

 

[Newdude]

If I change CYA to 30 there is no change to either recommendation. That response is one of the 2 reasons why I asked my question

So you just found a new poolamth bug. And THANKS. If the FC field is blank or 1, it doesn't matter what the CYA is and it doesn't calculate.




As soon as the FC is 2+, it works as it should.




Until we get this fixed, use the chart as a reference, or put values in both fields in the app with at least 2 FC.

 

[AUSpool]

PoolMath doesn’t consider or factor in your CyA level when calculating a FC dose. It is simply the difference between your “now” level of FC compared to your “target” level of FC. The calculated dose should raise your current FC to your desired FC target. The calculator uses your preselected pool volume and the %bleach. Each user must choose a desired target FC value from FC/CYA Levels and then set that as the target level.

For instance, I run at 7ppmFC/70ppmCyA through summer and 5ppmFC/50ppmCyA through winter so I change my target FC as required. Thats for an outdoor pool, I don’t have a hot tub. Other then the condo’s hot tub when skiing but thats managed for us.

 

[DougJack]

Hi, and thanks, but I'm not sure which one of you is correct. Is there a bug, or doesn't it change the recommendation based on CYA?

 

[DougJack]

Ok, I tried values other than my original example and understand that Pool Math doesn't consider CYA when recommending dosage. (I haven't gone through the math.) So now I have the more difficult issue for me to understand.:

The chemistry of CYA stabilized hot tubs says that CYA forms a reversible bond with HOCL. If it isn't saturated it will actually hold 95% of the FC in the hot tub or pool. If we just take those numbers at face value then at equilibrium there will be about 20 x more FC bound to CYA than is found by a DP measurement. From a practical point of view it is important to know how it gets there for dosing. It has to primarily come from the addition of Cl. The implication is that Pool Math, if it doesn't consider CYA, or at least approximate the impact a general impact it will have, will recommend considerably less liquid chlorine than it will actual take to hit the target. I have personally found that I have to add a lot more. Can someone weigh in?

 

[ajw22]

The FAS/DPD drop test shows Free Chlorine which is both active cholorine (HOCL) and reserve chlorine that is bound to the CYA.

Pool Math recommends Free Chlorine ranges considering CYA level. It is upon to you to decide what specific FC you want have.

PoolMath works quite well for thousands of users and I don’t understand what you are looking to understand. PoolMath is a calculator. Keep FC at 7.5% to 12% of CYA and you are good. PoolMath simply does the calculation for you. I use 10% which I can determine without using a calculator.

 

[PoolStored]

PoolMath works quite well for thousands of users

10s of thousands...

 

[DougJack]

I really like Pool Math. I was just trying to understand it. It calculates the recommended addition of Cl as if there was no CYA. This is accurate, I think, if there is no CYA. It isn't accurate if there is CYA.

The FAS/DPD drop test shows Free Chlorine which is both active cholorine (HOCL) and reserve chlorine that is bound to the CYA.

Pool Math recommends Free Chlorine ranges considering CYA level. It is upon to you to decide what specific FC you want have.

PoolMath works quite well for thousands of users and I don’t understand what you are looking to understand. PoolMath is a calculator. Keep FC at 7.5% to 12% of CYA and you are good. PoolMath simply does the calculation for you. I use 10% which I can determine without using a calculator.

The FAS/DPD drop test shows Free Chlorine which is both active cholorine (HOCL) and reserve chlorine that is bound to the CYA.

Pool Math recommends Free Chlorine ranges considering CYA level. It is upon to you to decide what specific FC you want have.

PoolMath works quite well for thousands of users and I don’t understand what you are looking to understand. PoolMath is a calculator. Keep FC at 7.5% to 12% of CYA and you are good. PoolMath simply does the calculation for you. I use 10% which I can determine without using a calculator.

I don't think so. I think it measures the unbonded FC + the disassociated FC, the bonded HOCL is unavailable. My pool math only calculates the amount of liquid chlorine to add as if CYA wasn't there (using the little box where you can temporarily type in numbers). I'm trying to understand the foundation of the chemistry the best I can with my current knowledge. My hot tub works great! I just love learning, and learning how things work and how to make them work better.

 

[DougJack]

PoolMath doesn’t consider or factor in your CyA level when calculating a FC dose. It is simply the difference between your “now” level of FC compared to your “target” level of FC. The calculated dose should raise your current FC to your desired FC target. The calculator uses your preselected pool volume and the %bleach. Each user must choose a desired target FC value from FC/CYA Levels and then set that as the target level.

For instance, I run at 7ppmFC/70ppmCyA through summer and 5ppmFC/50ppmCyA through winter so I change my target FC as required. Thats for an outdoor pool, I don’t have a hot tub. Other then the condo’s hot tub when skiing but thats managed for us.

Thanks for the note. I agree with you. What started my curiosity on this was when it took much more Cl to raise my FC than PM calculated. I had been trying at first to use Liquid Chlorine. I've since switched to a SWG, which has worked much better while I travel travel but I still had the basic question of why was the recommendation so far off for me..

 

[Newdude]

What started my curiosity on this was when it took much more Cl to raise my FC than PM calculated.

This is common and there are 2 reasons for it. Its not the CYA.

1) weak bleach
2) the tub is bigger than you think.

At any CYA level, XX bleach will raise you YY ppm as a constant. So PM doesn't tell you to add more ounces of bleach because the CYA is a 70 and not a 30. It DOES however, adjust the *recommended range* so you can decide if you should be at mid target, high target, etc.

Those daily recommeded ranges really don't mean anything for you anyway with a hot tub. You aren't losing a constant FC to the sun everyday in a covered spa. You might lose 4 ppm over an idle week, then blow through 6ppm three times on Saturday.

 

[ajw22]

I don't think so. I think it measures the unbonded FC + the disassociated FC, the bonded HOCL is unavailable.

Thst is not true.

Do your own science experiment instead of mental exercises.

Use the same liquid chlorine and add the same amount to 0 CYA water and 100 CYA water.

Test the two batches for FC. You will get the same results.

Your hot tub experience is not a sufficiently controlled sample to draw your conclusions.

 

[Newdude]

I played more with poolmath and it seems to want all 3 values added each time. (Current FC / CYA / target FC). If you just change the CYA without adding random #s for the other 2, the recommedation doesn't update. Sometimes entering new values for current FC and CYA will update the recommendations, but usually not without target FC.

I forwarded the bug up the chain with a PM and email.

I'd use the chart for now until you know what the levels should be from memory.

 

[AUSpool]

Both DPD and FAS/DPD tests measure the active FC, HOCl, the chlorinate ion, OCl-, and the chlorine bound to CyA as FC in ppm. More accurately the chlorine bound to CyA are chlorinated cyanurates. The reactions between HOCl and OCl-, and the reactions between HOCl and CyA are all equilibrium reactions that are in constant flux. As a little bit of HOCl is used roughly the same amount of Is “unbound” from the CyA maintaining equilibrium. Reaction rates or change in reactants and products to maintain equilibrium are very quick. Equilibrium is maintained but the ratio slowly changes as HOCl is used, the ratio is corrected when we add more FC.

Other then water volume and chlorine strength another big factor that will cause variations between calculated and measured FC is lingering bacteria, algae and general other waste that can use a significant potion of the added FC.

 

[DougJack]

This is common and there are 2 reasons for it. Its not the CYA.

1) weak bleach
2) the tub is bigger than you think.

At any CYA level, XX bleach will raise you YY ppm as a constant. So PM doesn't tell you to add more ounces of bleach because the CYA is a 70 and not a 30. It DOES however, adjust the *recommended range* so you can decide if you should be at mid target, high target, etc.

Those daily recommeded ranges really don't mean anything for you anyway with a hot tub. You aren't losing a constant FC to the sun everyday in a covered spa. You might lose 4 ppm over an idle week, then blow through 6ppm three times on Saturday.

Thanks, I have considered weak bleach and it is still a possibility. I have considered big dilutions to be able to measure strength. That might be fun/informative anyway. As to the tub volume, it is a Sundance Optima so there is a good chance it is close to accurate. I will try to estimate though. I should be able to easily see if it is within 20% and not 70% larger.

I understand a little of the dynamics of the CYA, and at these HOCL levels with as many bonding sites as it has and temp etc., there should be very little difference between the equilibrium percentages between say 30 and 70 ppm.

I'm traveling right now so I can't really try any experiments.

 

[DougJack]

Thst is not true.

Do your own science experiment instead of mental exercises.

Use the same liquid chlorine and add the same amount to 0 CYA water and 100 CYA water.

Test the two batches for FC. You will get the same results.

Your hot tub experience is not a sufficiently controlled sample to draw your conclusions.

That's a great idea. I'll do it when I get home.