CYA Levels: Conflicting Recommendations

ChrisA76 · Dec 1, 2022

Hi all, I spent the last three weeks reading up and devouring as much information as I can about the care of my 14,400 gallon salt water pool, from blogs, YouTube channels, a few books, and then also going back and forth with my own Taylor test kit as well as getting readings from Leslie's pools. With the help of Leslie's I solved a pretty serious algae problem and since then I've been keeping the chemicals pretty well balanced.

There seems to be little controversy over the recommended ranges for most of my water measurements: pH, TA, CH, Free and Total Chlorine.

But what is baffling is the conflicting recommendations about CYA levels.
Orenda Tech and Pulsar Systems, which are concerned about chlorine effectiveness, seem to suggest sticking around the 20-30 ppm (maximum). Other places (Leslie's), websites, and apps (TFP PoolMath for example) seem to suggest CYA levels upwards of 50 ppm.

However, I'm concerned about chlorine effectiveness. Quick google searches on "CYA effects on disinfection" seem to suggest that you get the most bang for the buck (in terms of UV protection) at 10 ppm CYA and above that it's diminishing returns. However, at CYA levels above 20 ppm you lose a lot of chlorine effectiveness for disinfection. Bob Lowry and Orenda Tech suggest that you need chlorine levels to be at least 7.5% of CYA levels, so at 60 ppm CYA you'd already need more than 4.5 ppm free chlorine! Pulsar Systems suggests the same, except they state it by this 14:1 ratio (CYA Effects on Disinfection - Pulsar Systems)

So what am I to think? Right now it's winter and I'm keeping my CYA at 20 ppm, but given that it's hard to lower CYA levels I am scared to go higher and have algae issues down the road. All the research I've done suggested that I'm near the sweet spot, but am I sure? Heck no.

Thoughts?

Newdude · Dec 1, 2022

Hey Chris and Welcome !!!

So you seem to have sorted out the parts that mattered from many sources. Bravo.

You got all the parts about diminishing returns with increasing CYA correct. What you missed was that with lower CYA, you lose the FC rapidly to the UV from the sun, and it's all for naught.

So first and foremost, you need to protect your FC, so it remains in the pool to sanitize. 30 is our starting point, but many need more in the warm climates, and even more in the hot climates.

Here we preach listening to your pool, because it will always tell you what you need. If your FC holds to the usual 2-4 ppm daily loss with a CYA of 30, then great. If not, add 10 and road test that for a week or two. Keep in mind, the daily loss throughout the season is like a bell curve and none of us are losing alot of FC these days with a low sun and short days. As the next season ramps up, you'll be testing daily and see it coming, and adjust as needed.

Everything we do here from a chemistry standpoint hinges on frequent, reliable testing. Great job with the Taylor kit, which one is it ? Some need an add on test (Fas/Dpd...... 'powder') to accurately test the FC above 3. The comparator block test isn't very accurate.

Newdude · Dec 1, 2022

Also..... we've gotten most of our 336k members the *exact* same way we got you. Problems led to confusion which led to more problems and a pool store was just delighted to sell them all KINDs of stuff they didn't need, usually only masking a big problem for a couple weeks, so it looked like a new problem next time.

I need you to perform an Overnight Chlorine Loss Test to verify your water is cured of the previous ailments. What you do is get the FC up to 8 or 10 and let it sit overnight. With no sun burning it off, you'll have the same FC in the morning if there is no organic matter in the water. Algae grows exponentially and the last couple of growth cycles is the difference between clean water with algae, and a swamp. Trust me it has fooled a bazillion folks to date.

So run the test, prove it's good, and we can get on with maintaining it going forward.

ChrisA76 · Dec 1, 2022

Thanks for the welcome! I really appreciate your quick response

At the risk of coming off as combative (I'm really not, just trying to assimilate all this information) on this:

What you missed was that with lower CYA, you lose the FC rapidly to the UV from the sun, and it's all for naught.

I didn't really miss it. What I was talking about is that according to sites like Pulsar (CYA Effects on Disinfection - Pulsar Systems),

it seems that most of the bang for the buck on UV protection is going to be from the first 10-20 ppm of CYA and after that it's diminishing returns. So I don't see why from this that 30 ppm CYA would be the starting point. It seems that given FC effectiveness vs. CYA that 30 should be closer to the max of what you want; You don't get much higher UV protection but you get a lot more loss of effective chlorine.

But I completely agree with listening to your pool and testing a lot and that's what I plan to do. I'd just like to have some idea of what to do before I hit the summer and I'm struggling to maintain the right levels of everything.

Yeah I got a Taylor K-2005 but I'm colorblind so instead of asking my wife every day to tell me which colors it looks like and, even then, getting accuracy only to the nearest 0.5 ppm I decided to splurge for a ColorQ 2x Pro 7. I got it on Leslie's for ~$200. Seems like a splurge now but I think the accuracy will pay for itself after a year.

ChrisA76 · Dec 1, 2022

Newdude said:
Also..... we've gotten most of our 336k members the *exact* same way we got you. Problems led to confusion which led to more problems and a pool store was just delighted to sell them all KINDs of stuff they didn't need, usually only masking a big problem for a couple weeks, so it looked like a new problem next time.

I need you to perform an Overnight Chlorine Loss Test to verify your water is cured of the previous ailments. What you do is get the FC up to 8 or 10 and let it sit overnight. With no sun burning it off, you'll have the same FC in the morning if there is no organic matter in the water. Algae grows exponentially and the last couple of growth cycles is the difference between clean water with algae, and a swamp. Trust me it has fooled a bazillion folks to date.

So run the test, prove it's good, and we can get on with maintaining it going forward.

This is awesome and interesting. I will read and try it. My tracking said that my ColorQ just arrived so I can try this tomorrow since I have some time to dedicate to it.

ChrisA76 · Dec 1, 2022

BTW, I also made a pretty nice spreadsheet with a lot of my findings from various sources, that includes a built-in computation of Langelier Saturation Index from pH, TA, CH, CYA and TDS, as well as a built-in computation chlorine effectiveness from the empirical charts I've found.

I'm a quantitative type so all this is fun for me. Once I get a little more confidence with it I might share it to the forum.

JoyfulNoise · Dec 1, 2022

If you’re interested in the chemistry rationale behind TFP, read through this -

Thread 'Pool Water Chemistry'
Pool Water Chemistry

This chart describes the effect of CYA on the half-life of chlorine.

When you fix the FC as a percentage of CYA as is suggested by TFP, you don’t have to worry about chlorine effectiveness (whatever that word means because it is not a technical definition). What matters is HOCl concentration and at 7.5% there is more than enough HOCl in the water to keep a pool sanitary and clean. As well, once CYA is present in the water, the pH dependency of active chlorine doesn’t matter much. Most of the chlorine is held in reserve and the rest splits into HOCl/OCl- and the level is high enough to be “effective”.

Most of the other sites you have found derived a lot of their recommendations from TFP and Richard Falk (aka, chem geek). Richard has a spreadsheet that does all the complicated calculations of pool water analysis from first principals. It’s not the easiest spreadsheet to use but it’s quite accurate.

Newdude · Dec 1, 2022

ChrisA76 said:
I'm a quantitative type so all this is fun for me

By all means, get your geek on. Head on over to the 'deep end' sub forum if you REALLY want to rabbit hole.

We gave up on LSI and focus on CSI. For vinyl and fiberglass it's much less of an issue. When you get a minute, Fill out your signature

TDS is the most meaningless stat. The parts make all the difference and the sum of the parts means nothing. Quick!!!! You have 37 items in your fridge. Do you have enough supplies for a weeks dinner, or do you need to shop asap ? It really depends if the items are on the shelves, or the fridge door, now doesn't it ?

ChrisA76 said:
built-in computation chlorine effectiveness from the empirical charts I've found.

Here is our easy chart. FC/CYA Levels
I prefer to run hot and target so that at an absolutely worst, I fall back into target range. Minimum is lava. Avoid it, or anything near it at all costs. If you're losing 4ppm in the peak season, you need to add at least 4ppm over minimum a day to remain in the clear. The chart is a start point, adjust as necessary.

In regards to your chart...... 20 CYA may be the sweet spot in a lab, but is night and day different in Buffalo or Miami.

ChrisA76 said:
Yeah I got a Taylor K-2005

Get a Fas/dpd. It makes your 2005 a 2006 The test goes from hot pink to clear and is no guessing.

ChrisA76 · Dec 1, 2022

JoyfulNoise said:
If you’re interested in the chemistry rationale behind TFP, read through this -

Thread 'Pool Water Chemistry'
Pool Water Chemistry

This chart describes the effect of CYA on the half-life of chlorine.

View attachment 464221

When you fix the FC as a percentage of CYA as is suggested by TFP, you don’t have to worry about chlorine effectiveness (whatever that word means because it is not a technical definition). What matters is HOCl concentration and at 7.5% there is more than enough HOCl in the water to keep a pool sanitary and clean. As well, once CYA is present in the water, the pH dependency of active chlorine doesn’t matter much. Most of the chlorine is held in reserve and the rest splits into HOCl/OCl- and the level is high enough to be “effective”.

Most of the other sites you have found derived a lot of their recommendations from TFP and Richard Falk (aka, chem geek). Richard has a spreadsheet that does all the complicated calculations of pool water analysis from first principals. It’s not the easiest spreadsheet to use but it’s quite accurate.

I was using "chlorine effectiveness" as a short-hand to mean HOCl concentration as per Bob Lowry and Pulsar's site. I'm also new to this so I might not have gotten the technical definitions correct, but the point seems to have gotten across.

It doesn't seem to me that there's a lot of difference in half-life between 20 ppm CYA and 50 ppm CYA, but I'm going to read through the pool water chemistry thread and make sure I understand it all before I comment fruther. I suppose 50 ppm CYA is reasonable but I can't see myself going higher than this based on my current understanding, and I prefer to slowly increase it since going higher will be a lot easier than dropping it later.

Newdude · Dec 1, 2022

ChrisA76 said:
, and I prefer to slowly increase it since going higher will be a lot easier than dropping it later.

Bingo.

Use what you've learned, to listen to your pool. If you find your pool to be doing great with a 20 CYA, then that's terrific. With a third of a million members spanning over 15 years, the collective wisdom is off the charts. The initial science has been tweaked further for climates and fill water sources.

But every pool in the land is still unique and we'll help you learn yours.

Here's our official rules.

Know where you are. (Trusty test kit)
Know where you want to be.
Know what to add.
Know what it will do.
Verify it did. (Full circle with trusty kit)

It doesn't get much easier than that. Read up and get as deep as you'd like. Ask away at any time.

ChrisA76 · Dec 1, 2022

Newdude said:
Bingo.

Use what you've learned, to listen to your pool. If you find your pool to be doing great with a 20 CYA, then that's terrific. With a third of a million members spanning over 15 years, the collective wisdom is off the charts. The initial science has been tweaked further for climates and fill water sources.

But every pool in the land is still unique and we'll help you learn yours.

Here's our official rules.

Know where you are. (Trusty test kit)
Know where you want to be.
Know what to add.
Know what it will do.
Verify it did. (Full circle with trusty kit)

It doesn't get much easier than that. Read up and get as deep as you'd like. Ask away at any time.

Thank you I do appreciate all the help so far. I am definitely going to get an FAS DPD test and perform the overnight chlorine loss test. I’m really excited to have found this forum.

PoolStored · Dec 1, 2022

We, and pool math use CSI.

A bit of the rationale:

CSI and LSI - Further Reading

www.troublefreepool.com

ChrisA76 · Dec 1, 2022

PoolStored said:
We, and pool math use CSI.

A bit of the rationale:

CSI and LSI - Further Reading

www.troublefreepool.com

Thank you for this

PoolStored · Dec 1, 2022

Newdude said:
In regards to your chart...... 20 CYA may be the sweet spot in a lab, but is night and day different in Buffalo or Miami.

Preach. Even with a CYA of 70 (NOTE MY POOL IS SWGC NOT CHLORINE), I can chew through 5.5 FC on a sunny day in J/J/A. Know when I know my CYA has degraded...when my chlorine consumption starts rising.

You will find if you are using liquid chlorine, you will use more at a lower CYA. I wouldn't hesitate to run a Liquid Chlorine pool at 60 CYA. The cost of LC has gone through the roof in many locations.

Home Depot Pool Chlorine

Anyone notice the price increase from $18 per case to $30? Unreal!

www.troublefreepool.com

JoyfulNoise · Dec 1, 2022

Depending on where you are in the East Bay, it can get very hot especially on the other side of the Berkeley Hills in Diablo Valley. 30ppm CYA will likely fail to keep the FC at an acceptable level and depending on how you plan to chlorinate (manual chlorination versus SWG), you could find yourself playing catch up all the time.

The thing to recognize about pool water chemistry, fancy charts, spreadsheets, and equilibrium chemistry equations is that they are all built on a mountain of assumptions. There is no exact solution. So as others have pointed out, you’re going to have to experiment. Your pool can’t be told how to react, it’s going to tell you. So, if you need to increase CYA to improve chlorine loss, do that. There is no sense in being caught in “chlorine effectiveness” arguments when the simplest answer is … just add more CYA and increase the FC to match it. You’re not cooking up rocket fuel, it’s a swimming pool, so try not to lose the forest for the trees … good luck.

ChrisA76 · Dec 1, 2022

JoyfulNoise said:
Depending on where you are in the East Bay, it can get very hot especially on the other side of the Berkeley Hills in Diablo Valley. 30ppm CYA will likely fail to keep the FC at an acceptable level and depending on how you plan to chlorinate (manual chlorination versus SWG), you could find yourself playing catch up all the time.

Yes it gets extremely hot but we do have a safety cover that’s on when not in use. It’s on 80% of the time or more during the summer daylight hours.

generessler · Dec 2, 2022

To complete the picture, my pool is on the other end of the spectrum because it's surrounded by a house and 40' evergreens. Even on a mid-August cloudless 95F North Carolina day, I lose ~2 ppm. These days it's 1 ppm every 3-4 days.

So your graph's "partly cloudy" is kind of a laughable measurement. The upshot is that @Newdude 's advice is spot on. Start with 30 (unless you have a swg; then start at 50). Measure. Adjust carefully. In fact everything about maintaining balance is the same. Measure. Use PoolMath to figure out any correction needed. When starting out, apply half that. Measure again. Keep records. In not much time you'll know how the pool will respond like it's a member of the family.

ChrisA76 · Dec 2, 2022

generessler said:
To complete the picture, my pool is on the other end of the spectrum because it's surrounded by a house and 40' evergreens. Even on a mid-August cloudless 95F North Carolina day, I lose ~2 ppm. These days it's 1 ppm every 3-4 days.

So your graph's "partly cloudy" is kind of a laughable measurement. The upshot is that @Newdude 's advice is spot on. Start with 30 (unless you have a swg; then start at 50). Measure. Adjust carefully. In fact everything about maintaining balance is the same. Measure. Use PoolMath to figure out any correction needed. When starting out, apply half that. Measure again. Keep records. In not much time you'll know how the pool will respond like it's a member of the family.

It’s not my graph. It’s from a site that I linked. I didn’t mean it to be “laughable” I’m just trying to learn.

Newdude · Dec 2, 2022

ChrisA76 said:
It’s not my graph. It’s from a site that I linked. I didn’t mean it to be “laughable” I’m just trying to learn

It's not you. We all know that. Just pointing out the real world flaws that aren't accounted for. None of us knew squat when we got here and were full of half truths or 'well yes, but no' situations. Or true things that were irrelevant, like TDS and TC.

You're doing GREAT.

generessler · Dec 2, 2022

ChrisA76 said:
It’s not my graph. It’s from a site that I linked. I didn’t mean it to be “laughable” I’m just trying to learn.

Absolutely no offense intended. 2.5 years ago I was just where you are. In the school of hard knocks I learned that a good 40% of what's "out there" about pools is misleading at best. Another 30% is questionable.

Otoh what I've read from folks here has never, ever let me down.

I was saying the person who elected to publish that chart was laughably naive if they expected "partly cloudy" would be useful in more than one location.

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