Where does my CYA go over the winter?

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wayner

wayner

LifeTime Supporter
May 31, 2012
855
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
Every spring when I open my pool my CYA is way down, often too low to measure. What happens to it? I tested my CYA over the weekend and the black dot is still clearly visible even though I have one of the tall tubes that has a reading down to 20 - so I am somewhere less than 20.

I thought that CYA stays in your pool and only goes down when you drain and refill. But this has not been my experience.
 
When you close, do you use a solid or a mesh cover? We use a mesh cover and our CYA typically disappears over the winter. I know it breaks down slowly over time, and we drain out down below the returns and let snow/rain refill it, so I know our CYA drops from that as well.
 
CYA will degrade in pool water over the winter.

From CYA - Further Reading

How is CYA Lost and Degrade in Pool Water?​

In general, once you add CYA to pool water it will be in the water unless you drain the water that contains the CYA. Some CYA is lost as water splashes out from pools.

Water leaking from pools will take CYA with it. Unexplained dropping of CYA levels, especially if you have an auto-fill automatically adding fresh water to the pool, can indicate a water leak.

Evaporation of water from the surface of the pool will not cause a loss of CYA. The water will evaporate and the CYA will stay in the remaining water.

High pool water temperatures will cause the chlorine to oxidize Cyanuric Acid. This tends to show in water temperatures of 90+ degrees. Every 10F increase in temperature results in roughly doubling the rate of degradation.[8]

Chlorine breakdown in sunlight causes CYA degradation by hydroxyl radicals. This can cause a loss from 2 ppm per month to 10 ppm per month depending on the amount of sunlight the pool is exposed to.

In an area with 90+ pool water temperatures and extreme sunlight exposure 10+ ppm of CYA a month can be lost through degradation.

There is bacteria that feeds on Cyanuric Acid and will create ammonia in pool water. This can only occur if the Free Chlorine falls to 0 allowing the bacteria to live. This generally happens in pools closed for the winter and discovered at pool opening.
 
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Hey Wayner and welcome back !!!

CYA degrades between 3 and 5 ppm a month. Not noticeable month to month, and certainly not helpful if you were using tabs and it's a 170, but if you walk away for 6 months, you'll see it for sure.

Also, you drained some for closing replaced with rain or opening fill. A foot, for example, is about 1/5 of the average depth of a typical inground pool.

Also also, if you have a permeable cover like a mesh looplock, 2- 3 ft of rain in the off season added up as well for some serious dillition. I lost about 50 each winter from all of the above.
 
What is your water temp now?

CYA Testing - Further Reading

www.troublefreepool.com www.troublefreepool.com

Cold Test Water Should be Room Temperature for CYA Test​

If the water temperature is below 70F degrees let the water warm up inside before you do the CYA test.

The standard instructions to mix for 30 seconds is not enough time when the water is cold. You can either mix longer, or allow the sample to warm up to room temperature. Best solution is to allow the the sample to warm up first and then shake it for 30 seconds.[4]

Taylor Technologies has run the pH, total alkalinity, calcium hardness, free chlorine, and cyanuric acid tests on known standard solutions at approximately 104°F, 75°F, 60°F, and 40°F. Only at 40°F did the CYA standard solution test higher than its actual value (after accounting for test variability). All other tests were unaffected by temperature differences.[5]

The melamine solution that is used in the better tests is at low pH so as to force the maximum precipitation of melamine cyanurate since it is somewhat soluble at pH 7.0 with a solubility of around 20 ppm. There is no question that at colder temperatures it will take longer to precipitate.[6]
 
Oly said:
What is your water temp now?
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That brings up *2* great points. The cold pool water takes longer to mix up in the vial and speaking of mixing........ the pool needs a good mixing before testing.

Letting the pump run for a day and letting the sample warm to room temperature may add some missing ppms.
 
Thanks for the replies folks. Yes, I would expect dilution as some water is drained when the pool is winterized and then over the winter the pool fills up with rain and snow.

When I did the CYA test on the weekend the water temperature was 56F. It will now be up into the 60s as the weather is warming up. I will try taking a sample inside to let it warm for a while.

So maybe the low temperature is an issue as well. I did add about 1.75 kg of dry stabilizer this weekend.
 
Newdude said:
That brings up *2* great points. The cold pool water takes longer to mix up in the vial and speaking of mixing........ the pool needs a good mixing before testing.

Letting the pump run for a day and letting the sample warm to room temperature may add some missing ppms.
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My filter had been running for several days before I tested the CYA and I waited until the water was clear - which generally takes about 3-4 days for my pool.
 
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Just tested for CYA again. Ambient water temp is now up to 63F. I let the sample warm up for a while but I am still reading around 21 despite the warmer temperature and giving three more days for the 1.75kg of CYA that I added a few days ago to be dissolved into the pool.
 

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I have the tall tube that goes up to 20. I am pretty sure that I bought it at TFTestkits a couple of years ago. Here is a link: https://tftestkits.net/images/products/1205.jpg The problem is that you go through a lot of CYA reagent when the level is that low as you need about 15mL of each water and the reagent.
cya tube.jpg
 
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You can’t read between lines - the scale is logarithmic, not linear. So just round up. If it’s visible at 30 but disappears before you get to 20, just call it 30. It’s close enough for what we do. :)
 
IceShadow said:
You can’t read between lines - the scale is logarithmic, not linear. So just round up. If it’s visible at 30 but disappears before you get to 20, just call it 30. It’s close enough for what we do. :)
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Ok, I was doing kind of a logarithmic interpolation as the gap between 20 and 30 is very wide. But 20 or 30 is good enough. The margin of error on this test has to be huge as it is so subjective as to when the dot disappears and I presume it can be very dependent on ambient light, distance from your eye, quality of your eyesight, etc.
 
The CYA can be unreliable if the water sample is too cold (60F or 65, I’m never sure). When I opened the pool my water was 54F and there was over 10pm difference between testing with cold water and heating up the sample before the test.
 
wayner said:
Ok, I was doing kind of a logarithmic interpolation as the gap between 20 and 30 is very wide. But 20 or 30 is good enough. The margin of error on this test has to be huge as it is so subjective as to when the dot disappears and I presume it can be very dependent on ambient light, distance from your eye, quality of your eyesight, etc.
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What really has helped with consistency in my readings is to not stare at dot and fill, but rather, hold the vial up and fill to line, starting with a high number, lower to waist and look for dot, if see it, raise it back up and fill to next line, lower and look for dot..... repeat until you fill a line and no dot. If you want to round up, repeat procedure at half-way between the two readings and round up if needed.
 
CYA does actually degrade just way more slowly than FC. Certain kinds of soil bacteria in the genus pseudomonas genus will metabolize it also. Many people report that pools opened after the winter have low or 0 CYA and I suspect that pseudomonas may have a role. If this is the case you can also have some ammonia which is one of the by products. This will consume a LOT of FC until you react all of the ammonia out.
 
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