Are CYA readings easier to read at levels greater than 50 than below 50?; plus inquiry effects of adding CYA? CYA raised much more than anticipated.

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J

jmb

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May 26, 2011
41
Windsor Ontario Canada;SW Ontario near Detroit, MI
Pool Size
36000
Surface
Vinyl
Chlorine
Liquid Chlorine
We are getting close to closing our pool for the season and added dry stabilizer to increase our CYA from 30 to 40. We had been running CYA most of the summer at what we thought was 30 CYA per TFT pool test kit. We only use liquid chlorine and do not use pucks or other stabilizer. Gradually over the course of the summer the CYA dropped to 20 from rain and adding water due to evaporation. In mid August we added 1500 grams of dry stabilizer to raise CYA back to 30. Per Pool Math 1500 grams for our pool should raise the CYA by 11 which it did. At the end of August we added another 1500 grams of dry stabilizer to bring CYA up to 40 to 50 which I understand is the correct CYA for closing a pool with a mesh cover. When we tested the CYA today the reading was 70. According to Pool Math the CYA reading should have been 40 no more than 50. I am trying to figure out how this happened.
I have 2 questions;
1. I understand CYA levels can be tricky to interpret but I am curious to know if for some reason it is easier to interpret CYA readings at higher CYA levels than at lower CYA levels. It looked like 30 when we started adding dry stabilizer. We actually recorded 30 because the reading was between 20 and 30 and I have read that in this case you should go up to the next number.
2. Did we add too much dry stabilizer over too short a period of time?
 
How soon after you added the stabilizer did you check your CYA levels? Some people say you might need 24-48 hours after it's all dissolved before finally seeing your CYA.. for me, it seems I get enough water movement that even 4 hours later the reading is the same as it will be 48-72 hours later but YMMV?
 
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In mid August I waited at least 5 days to test CYA. After 5 days my CYA raised as expected from about 20 to 30. In late August after adding the additional 1500 grams to raise my CYA from 30-40 we retested after about 5 days and the CYA was about 40. We retested agin after about 9 days to determine what are SLAM level should be to prepare for closing. That is when we got a reading of 70. We run our pool pump for 12 hours a day. While we were adding stabilizer we let it run for longer periods until the stabilizer dissolved.
 
jmb said:
We are getting close to closing our pool for the season and added dry stabilizer to increase our CYA from 30 to 40. We had been running CYA most of the summer at what we thought was 30 CYA per TFT pool test kit. We only use liquid chlorine and do not use pucks or other stabilizer. Gradually over the course of the summer the CYA dropped to 20 from rain and adding water due to evaporation. In mid August we added 1500 grams of dry stabilizer to raise CYA back to 30. Per Pool Math 1500 grams for our pool should raise the CYA by 11 which it did. At the end of August we added another 1500 grams of dry stabilizer to bring CYA up to 40 to 50 which I understand is the correct CYA for closing a pool with a mesh cover. When we tested the CYA today the reading was 70. According to Pool Math the CYA reading should have been 40 no more than 50. I am trying to figure out how this happened.
I have 2 questions;
1. I understand CYA levels can be tricky to interpret but I am curious to know if for some reason it is easier to interpret CYA readings at higher CYA levels than at lower CYA levels. It looked like 30 when we started adding dry stabilizer. We actually recorded 30 because the reading was between 20 and 30 and I have read that in this case you should go up to the next number.
2. Did we add too much dry stabilizer over too short a period of time?
Click to expand...

Water evaporates, cyanuric acid doesn't.

If adding water to replace evaporation, you don't need to add more CYA: as the water evaporates, CYA will increase. Then replacing the evaporation will bring CYA back to what it was.

Draining water away is obviously totally different.
 
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NaiNot said:
Water evaporates, cyanuric acid doesn't.

If adding water to replace evaporation, you don't need to add more CYA: as the water evaporates, CYA will increase. Then replacing the evaporation will bring CYA back to what it was.

Draining water away is obviously totally different.
Click to expand...
Thank you for your reply. I appreciate the information.
 
To answer your question, no, CYA testing is not easier in the higher end of the range. If anything I think maybe there is more confidence in the result in the 30 - 60ppm range where the gaps between each measurement are farther apart. Try not to agonize over the fine detail, the disappearing dot test can be tricky as you say but we really don‘t need to be supper acurite.

I’ve always used the fill to the line method and just look once. I know roughly where I should be from by records so I fill to 60, see dot, fill to 50, dot gone, 60ppm it is. And you can tip it back and do it again when that pesky cloud has gone or if you stated to low. I found it useful to practice with a 50ppm standard (R7065) which is not to hard to find. Pics of the dots and CYA testing tips are found in the wiki here.

Check your pool volume, your sig says your pool is 36,000g but a 20’x40’x4’ pool is 23,900g. That may be why you’ve over dosed a little. Switching from metric an imperial can be a source of error. Now that your up at 70ppm it’s no big deal, just use that to set your FC. A lot of closed pools loose CYA over winter so just test again when you open In spring.
 
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I’ve always used the fill to the line method and just look once.
AUSpool said:
To answer your question, no, CYA testing is not easier in the higher end of the range. If anything I think maybe there is more confidence in the result in the 30 - 60ppm range where the gaps between each measurement are farther apart. Try not to agonize over the fine detail, the disappearing dot test can be tricky as you say but we really don‘t need to be supper acurite.

I’ve always used the fill to the line method and just look once. I know roughly where I should be from by records so I fill to 60, see dot, fill to 50, dot gone, 60ppm it is. And you can tip it back and do it again when that pesky cloud has gone or if you stated to low. I found it useful to practice with a 50ppm standard (R7065) which is not to hard to find. Pics of the dots and CYA testing tips are found in the wiki here.

Check your pool volume, your sig says your pool is 36,000g but a 20’x40’x4’ pool is 23,900g. That may be why you’ve over dosed a little. Switching from metric an imperial can be a source of error. Now that your up at 70ppm it’s no big deal, just use that to set your FC. A lot of closed pools loose CYA over winter so just test again when you open In spring.
Click to expand...
Thank you for your reply. I have used the 50 ppm standard that you mention and it is helpful as a guide. Using the standard the black dot is obscured but I can still see the black dot so I aim for something between complete obscurity and what I see using the 50 ppm standard. I have purchased fresh 50 ppm standard a couple of times but I get the same results. I am feeling much more confident in my readings. I have also been using your method of "fill to the line and just look once" and have found that to be helpful. Our pool has a deep end ; it is 20' x40' x4' at one end and gradually gets deeper to 20'x40 x about 9.5' to 10' at the deep end. I will look at fixing that in my signature. Thanks again for your input and the link to the CYA testing tips!


AUSpool said:
To answer your question, no, CYA testing is not easier in the higher end of the range. If anything I think maybe there is more confidence in the result in the 30 - 60ppm range where the gaps between each measurement are farther apart. Try not to agonize over the fine detail, the disappearing dot test can be tricky as you say but we really don‘t need to be supper acurite.

I’ve always used the fill to the line method and just look once. I know roughly where I should be from by records so I fill to 60, see dot, fill to 50, dot gone, 60ppm it is. And you can tip it back and do it again when that pesky cloud has gone or if you stated to low. I found it useful to practice with a 50ppm standard (R7065) which is not to hard to find. Pics of the dots and CYA testing tips are found in the wiki here.

Check your pool volume, your sig says your pool is 36,000g but a 20’x40’x4’ pool is 23,900g. That may be why you’ve over dosed a little. Switching from metric an imperial can be a source of error. Now that your up at 70ppm it’s no big deal, just use that to set your FC. A lot of closed pools loose CYA over winter so just test again when you open In spring.
Click to expand...
 
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