Ahhh... the CYA test is driving me nuts

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Brett S

Well-known member
Mar 15, 2019
729
Orlando
I just filled my new pool. According to the manufacturer it holds 14364 gallons. After filling the pool I added 7 pounds of dry CYA and let it dissolve. According to pool math 7 pounds of stabilizer in 14364 gallons should put my CYA level at about 58. The directions on the product show numbers very close to what pool math predicted.

However, I just tested the CYA twice this morning with the taylor test kit and the first time I could see the dot at 90 and it had all but completely disappeared at 80. The second time I thought it was a bit more visible at 80, but it was completely gone at 70. I’m doing the test according to what I believe are the best practices - Outside on a sunny day with my back to the sun, so the reading is being done in the shade of my body. Holding the indicator at waist level and taking the reading quickly without staring at it too much.

Given the fact that this is all new water in the pool and that I’ve added a known amount of CYA I think it’s pretty likely that the level is actually pretty close to 60, but I’m a little concerned that I’m reading 70-80, so this makes me wonder if I’m doing something wrong as I read the test.
 
Chances are your pool volume is less than "14364" gallons. Sometimes manufacturers state the gallons based on filling the vessel up to the very top (near overflowing).

Are you doing the test outdoors, back to the sun, holding the vial at waist level? Don't stare at the dot... fill tube to 90, glance at the dot, see it, fill to 80, glance again. Still see it? Fill to 70, glance at the dot. Repeat as needed. If dot is visible at 70 and not at 60, round up and use 70 as your CYA level. The test accuracy is +/- 10 points.

You can use the same testing solution again during the same session. Do the test, note the result, pour the solution back into the bottle and do the test again. Do it 3 times and take the average of the 3 tests. Close enough, note the result.
 
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Let’s step back and look at the big photo and I suspect you’ll be less worried. Let’s assume your CYA is at 60, your FC target will be 3-9ppm with your SWG. Now let’s assume your CYA is at 80, your FC range will be between 4-11ppm. Notice the minimum level only went up by one part per million. Even the target FC number only goes up two.

If this were me personally I’d simply assume for the next week or so is at 80 and aim for a chlorine level around 6. Retest in a week or two and adjust from there. In the mean time, enjoy a few swims!
 
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proavia said:
Chances are your pool volume is less than "14364" gallons. Sometimes manufacturers state the gallons based on filling the vessel up to the very top (near overflowing).
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I believe that the 14364 number is an accurate number. It was listed as 14364 Gallons at 90%

Leebo said:
Let’s step back and look at the big photo and I suspect you’ll be less worried. Let’s assume your CYA is at 60, your FC target will be 3-9ppm with your SWG. Now let’s assume your CYA is at 80, your FC range will be between 4-11ppm. Notice the minimum level only went up by one part per million. Even the target FC number only goes up two.
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That’s true, it’s not a really but difference, but I am a little concerned because I know the Intex SWG I’m using is not a super powerful one. I’m afraid that it might have a hard time keeping up with the FC loss in the middle of summer here, so I think I’ll need all the CYA I can get. For now though, it’s keeping up just fine running four hours a day.

In the mean time, enjoy a few swims!
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Unfortunately that’s not going to happen for a little while... the water temp has been around 60-64 degrees:(. It’s been rather cold here lately and dropping into the 40’s at night. We’re supposed to get a few warm days next week and I’m hoping that might warm up the water enough for a swim though.
 
You’ve already got the mass majority of pool owners beat as having the pool setup this time of the year will allow you to tinker and fine tune things without the sun crushing you. By April once the rays really start to consume the FC you’ll have things all dialed in. There is a good chance the Intex SWG will need some help, but some liquid chlorine will come in handy during those times.

I hear ya about the weather as last week I was teased with 50-60 degree temps almost all week. Yesterday, about an inch of snow. ?
 
With a new fill, adding 7 lbs to your volume should result in a CYA of about 60, so I would go with that for now and not beat yourself up. You'll go nuts. :crazy: I know us TFP'ers get a bit OCD and like to see consistent, expected results, but I'd treat the pool as a CYA 60 and balance accordingly for now. Let things continue to mix well and perhaps test again later this weekend. As noted above ... don't stare at the dot. Just a quick glance > add more mixed reagent > glance again > add more mixed reagent if necessary > and repeat. After your final result, pour the solution back into the squirting bottle and do it a couple more times.
 
Brett S said:
Unfortunately that’s not going to happen for a little while... the water temp has been around 60-64 degrees:(. It’s been rather cold here lately and dropping into the 40’s at night. We’re supposed to get a few warm days next week and I’m hoping that might warm up the water enough for a swim though.
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I know, right? Its been chilly; good grief, I had frost on the ground this morning. I think Im going to pack up and move to Florida!! Oh wait.....
 

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markayash said:
Maybe thats why mine is off..My CYA was around 100 and I drained 75% of the water and retested and it showed 90!
I will let the water warm up inside and retest
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Not to get side-tracked on Brett's thread here, but in your case the CYA may have been higher than you originally thought. Trying to estimate a CYA over 100 can get tricky if not performed correctly. But yes, good point to bring the water sample indoors for about 30 minutes in the winter to allow chilly water temps to increase to at least 70 degrees.
 
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Keep in mind you can also buy CYA standards that come with 50 ppm CYA. You can use these to check your testing technique and see what the dot looks like at a known CYA level.
 
Brett S said:
believe that the 14364 number is an accurate number. It was listed as 14364 Gallons at 90%
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quite honesty those should be taken with a grain of salt, a few people have proved the actual volume is less
my own 12x24x52 is spiced at 32k litres@90% but is around 26/27k litres measured and those numbers work for chemicals. I’ll bet you are closer to 13k gallons at a real working water depth.
90% would be 90% of the 52” depth and I bet you don’t have 47” of water in the pool :)
 
a little late to the party
but with calcium, salt and cya only add 2/3 the amount required
then after a few days retest and adjust as required
never add a large amount at once as these are hard to reduce
after a while you will get to know your pool and have a better idea how it reacts to chemicals
 
I just did my CYA test after letting the pool water warm up and its around 40 now..When it was cold looked closer to 90 :) Once the water is balanced I will bring it up very very slowly until I get to the SWG recommended range :)
 
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