CYA and Chlorine Amounts

[clem1985]

Does higher CYA actually require more Chlorine use? Wouldn't it be only the initial dose of Chlorine to reach the levels required based on CYA levels that requires more , then after that its just replacing any FC loss? Which would be the same amount for Loss of FC with low CYA? Sorry for the very basic understanding of the concept of CYA/FC. I'm no chem guy and am entirely new to the TFP method.

 

[mguzzy]

No problem... If you want to be overwhelmed with the chem side of stuff, search for the posts by the chemgeek, there are many. Basically it was realized from a paper back in 1974 that there was a relationship between the CYA and FC levels in a pool and it resulted in FC/CYA Levels. The CYA buffers the chlorine to keep it from degrading in UV light. But it now takes a higher level of Cl to reach the same level of sanitation as you would without CYA. So the two go hand in hand. Since its harder to adjust CYA on a day by day basis, we adjust the FC to match your CYA level.. Does that make sense? Theoretically if you are at a higher FC level.. you lose the same FC even if you are at a low FC level.. but that isn't quite the same because the CYA comes into play.

 

[clem1985]

No problem... If you want to be overwhelmed with the chem side of stuff, search for the posts by the chemgeek, there are many. Basically it was realized from a paper back in 1974 that there was a relationship between the CYA and FC levels in a pool and it resulted in FC/CYA Levels. The CYA buffers the chlorine to keep it from degrading in UV light. But it now takes a higher level of Cl to reach the same level of sanitation as you would without CYA. So the two go hand in hand. Since its harder to adjust CYA on a day by day basis, we adjust the FC to match your CYA level.. Does that make sense? Theoretically if you are at a higher FC level.. you lose the same FC even if you are at a low FC level.. but that isn't quite the same because the CYA comes into play.

Thanks, I guess I'm looking at if from strictly a Money aspect, and what I cost to run a pool.

 

[Rancho Cost-a-Lotta]

One downside to higher CYA levels is the amount of chlorine required should a SLAM be necessary. Check out SLAM FC level requirements.

 

[mguzzy]

Thanks, I guess I'm looking at if from strictly a Money aspect, and what I cost to run a pool.

Depends on how you chlorinate. I have a SWG.. so excluding the upfront cost of that I spend at most a couple of hundred dollars a year tops. CYA costs me maybe 20 bux a year.. but I buy it 25 pounds at time and I can get a few years out of usually because its one of the chems that stores well. .. I'm not sure how to factor the cost of liquid Cl since its been so long since I did that dance.

 

[mgtfp]

Does higher CYA actually require more Chlorine use? Wouldn't it be only the initial dose of Chlorine to reach the levels required based on CYA levels that requires more , then after that its just replacing any FC loss? Which would be the same amount for Loss of FC with low CYA? Sorry for the very basic understanding of the concept of CYA/FC. I'm no chem guy and am entirely new to the TFP method.

The UV-protection improves more than linear with increasing CYA-level. That means that at higher CYA level you will loose less chlorine per day, even though you'll have to maintain a higher FC-level to have the same FC/CYA ratio, which is required to get the same sanitation effect out of the chlorine. Of course you'll need some chlorine to get to the higher level, but then you'll need to add less chlorine per day to maintain this level.

There were some experiments done a few years back:

Thread 'CYA Testing Update'

The problem with higher CYA is that you'd need to maintain very high FC levels should you ever have to SLAM your pool. That's why TFP recommends higher CYA (up to 80ppm) only for SWG-pools, where the constant and regular chlorination makes an algae outbreak less likely.

In manually chlorinated pools (with liquid chlorine) there is a higher risk for things going pear shaped, and TFP recommends lower CYA levels for these.

 

[BenB]

Wouldn't it be only the initial dose of Chlorine to reach the levels required based on CYA levels that requires more , the

I think the direct answer to the question you're asking here is "yes". You need some extra chlorine to get up to the elevated (above what the traditional level might be), but then the amount you add to maintain each day is no different.

So TFC is using higher levels of FC, but that doesn't mean adding more each day (and more expense). Indeed, following the methodology will be cheaper as you won't also be buying any side potions that might otherwise be pushed on you.

Above is mentioned that higher CYA will lead to lower FC loss per day so in reality it might be even better than equal.

Does higher CYA actually require more Chlorine use?

Based on the above, the answer to this is "no".

 

[Oly]

Your daily FC loss will increase if your CYA is too low or if your FC level is high and well above your target range for your CYA. FC loss also increases with more swimmers or high bio load. You are correct that your daily FC loss is the same if managed relative to your CYA level. Having to SLAM if needed changes things with high CYA.

 

[port1]

Such an excellent forum. There's nothing left to doubt when studying the replies to questions. One of the best forums on the 'net.

 

[Drd]

Depends on how you chlorinate. I have a SWG.. so excluding the upfront cost of that I spend at most a couple of hundred dollars a year tops. CYA costs me maybe 20 bux a year.. but I buy it 25 pounds at time and I can get a few years out of usually because its one of the chems that stores well. .. I'm not sure how to factor the cost of liquid Cl since its been so long since I did that dance.

I just bought a gal of liquid CYA 11/2022 albeit from Lesilie's, cost 50.00 and it's not pure CYA as it has been liquified. One gal will provide 32ppm CYA to 10,000 gal pool (concentration 30% CYA/4 oz = 1ppm CYA). Upside immediate results and can swim in 15 mins. When you are going through chlorine and find you have no FC on testing and starting to get yellow algae, immediate is best IMO. It worked too. I too am trying to figure out what is best on levels of CYA too 10-30/30-50/50-80?

 

[Gary Davis]

Does higher CYA actually require more Chlorine use? Wouldn't it be only the initial dose of Chlorine to reach the levels required based on CYA levels that requires more , then after that its just replacing any FC loss?

I keep my CYA low, at around 30ppm, because that makes my chlorine (at whatever level) more effective (yes, I know about the 7.5%); but I had never thought about the question of what the CYA level has on the AMOUNT of chlorine lost per day until I saw this thread just now - so I thank the OP for bringing up the question.

I think most of us strive to keep a low CYA level (with 30 ppm being low & 100 ppm being high), don't we?
The question then to ask ourselves, is why.

Of course, the simplistic answer is obvious - which is that the more CYA in PPM the better the sunlight protection.
But that comes at a cost, does it not (otherwise we'd all have 1,000PPM or more of CYA).

As I understand it, the curve is pretty flat from around 30 ppm to around 100ppm, which is why that's the typical range, right?
But then we have to ask what's the LOSS of FC at the low end (30 PPM CYA) and high end (100 PPM CYA) in that range?

• Is the FC loss linear within that 30 ppm to 100 ppm CYA range?
• Is it non-linear?
• Is it flat?

I don't know.

Do you?​

To the OP's question of "why", isn't his question basically (for an outdoor, uncovered, sunlit pool)...

• How much FC is lost per day with a low or high CYA level?
  
  • Hmmm..... I don't know.
  • I don't even know if we'd mreasure that loss in FC PPM or in percentage of FC PPM.

I guess the way I'd approach the answer is to consider the implications of the CYA level, most of which have been covered in this thread.

• The daily FC level is higher the higher the CYA (due to the 7.5% factor)
• The SLAM level of FC is higher the higher the CYA
• The pH effect on chlorine sanitation is almost non existent; hence the water pH can be realistically ignored
• The calcium saturation balance is slightly negatively affected by higher levels of CYA (but CSI can be adjusted by other means)

So what's DIFFERENT with a low CYA versus a high CYA?

• I'm assuming that a low CYA has a worse degradation of FC due to sunlight alone???

How much worse is a low CYA (30ppm) in terms of FC degradation than a high CYA (100ppm)?

• If it's only slightly worse, then we are all likely better off with a low CYA
• If it's greatly worse, then a higher CYA may save appreciable FC levels from sunlight degradation

I haven't thought about this before but the question must have been asked before since it's a perfectly valid question to ponder.

Assuming we keep our FC at least at 7.5% of the CYA level...

• At 30ppm CYA, how much FC is lost per day due to sunlight degradation?
• At 100ppm CYA, how much FC is lost per day due to sunlight degradation?

Can someone point me to a reliable chart with that answer?

 

[PoolStored]

Can someone point me to a reliable chart with that answer?

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[Bperry]

Of course, the simplistic answer is obvious - which is that the more CYA in PPM the better the sunlight protection.
But that comes at a cost, does it not (otherwise we'd all have 1,000PPM or more of CYA

You’de have a hard time measuring pH with the increased chlorine that 1000ppm of CYA would require.

 

[mgtfp]

But then we have to ask what's the LOSS of FC at the low end (30 PPM CYA) and high end (100 PPM CYA) in that range?

• Is the FC loss linear within that 30 ppm to 100 ppm CYA range?
• Is it non-linear?
• Is it flat?

I don't know.
Do you?

UV protection increases more than expected just by the proportion of FC bound to CYA, which is the basis of the curves calculated by Chem Geek that @PoolStored posted. Chem Geek highlights a couple of times in this thread that there is an additional shielding effect that is harder to quantify.

@mas985 did a number of tests over the years confirming that, here the latest results, also with a link to older results:

CYA vs UV Chlorine Loss Test Update

Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now...

www.troublefreepool.com

With an SWG, TFP recommends to take advantage of the better protection at higher CyA levels.

Without SWG, you are at higher risk of missing to add chlorine sooner or later, and the risk of having to SLAM has to be weighed against the better UV protection at higher CYA levels. And SLAMing at CYA 80ppm is not much fun, therefore TFP recommends lower CYA targets for LC pools.

(otherwise we'd all have 1,000PPM or more of CYA).

You also need to consider that FC oxidizing CYA is one of causes of chlorine loss without UV, contributing for example to overnight chlorine losses even without algae, which is why the criteria for a successful OCLT is not set to zero loss.

At some point (certainly below 1000ppm), the improved UV protection of higher CYA levels will get over-compensated by FC losses due to CYA oxidation.

Plus, to maintain an FC/CYA ratio of let's say 10%, you needed to target an FC of 100ppm. Daily losses of let's say 20% (which would be about 2ppm loss at FC 10ppm), would result in daily losses of 20ppm. These are insane amounts of chlorine to be added daily to start with, and you couldn't ignore the big pH swings caused by adding and using chlorine any longer. And I assume that 20% daily FC loss would be very optimistic. I reckon that above mentioned losses due to CYA oxidation would be very significant.

And the only fix for an algae bloom at CYA 1000ppm would be a 100% drain-refill.

And at these levels you also needed to consider effects of CYA on human (and pet and wildlife) health.