Some questions /thoughts about CYA

A_kraker99

Well-known member
Jul 18, 2015
103
Zeeland MI
So my pool just started getting cloudy yesterday which I assume was an algae bloom since all my other levels seem to be in check. It was a surprise to me because I thought my CYA was around 35-40 and I haven't let the FC go below 3. That got me questioning my CYA levels again. Cue the super easily mis-interperted CYA black dot test. I read a little bit about the test and shook the solution for 30 seconds, let it sit for a couple of minutes and then did the test with my back to the sun. Does this sound like a good procedure? When I do this it seems as if the black dot disappears around the 50 mark on the vial. If I have the vial in the sunlight I can see the black do till around 35-40.

Anyway, comment on what you think about my CYA level above. Should I use the sunlight reading or back to the sun reading? Here are my other questions.
1. CYA is meant to protect Chlorine from the sun burning it up right? So if I had a CYA of 30 and kept my FC at 4 vs having a CYA of 50 and keeping FC at 6, I would actually use less chlorine with the latter option even though I have to maintain a higher level of FC, correct?
2. A FC level of 6 still seems really high to me. I am almost scared to maintain it so high! Maybe that is just from seeing all the crappy tests on the market recommending 1-4 all the time? I am brainwashed to think that amount of chlorine is absurdly high. My skin seemed to dry out already with maintaining a level of 4. Any words of comfort here?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,868
Laughlin, NV
From the CYA testing directions in Pool School: "Stand outdoors with your back to the sun and hold the view tube at about waist level. If sunlight is not available, find the brightest artificial light you can."
So use the back to the sun number.
1. -- to a point. For a non-SWCG pool a CYA of 50 ppm is the highest we like to recommend. Especially in your location.
2. FC level up to SLAM level has little to do with skin irritation, eye irritation, etc. That is typically from out of range pH and / or CC in the water. With a CYA of 50 that you have, if you did not know the FC level, you would not know the difference between target FC of 8 ppm or 16 ppm.
 
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A_kraker99

Well-known member
Jul 18, 2015
103
Zeeland MI
I have the PoolMath app on my phone. With CYA at 50 it shows a target of 4.0-8.0 That app was developed from someone here right? Are you saying a target of 8 because you like to keep it at the higher end of the recommended range? Should I aim for 8 when adding chlorine so that during the day it never gets below 4? I actually use a dosing pump scheduled twice a day to run for a few minutes to try to keep a more consistent level.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,932
San Dimas, CA (LA County)
I have the PoolMath app on my phone. With CYA at 50 it shows a target of 4.0-8.0 That app was developed from someone here right? Are you saying a target of 8 because you like to keep it at the higher end of the recommended range? Should I aim for 8 when adding chlorine so that during the day it never gets below 4? I actually use a dosing pump scheduled twice a day to run for a few minutes to try to keep a more consistent level.
Your personal target can only be determined by testing. You want enough FC in there so that you don't dip below minimum before the next bleach addition. So if you're programmed to add twice a day, test just before and see where you're at. Both times. If you never dip below 5, you can target a little lower. If you find you dip below 4, you need to increase. The key is to never dip below minimum and keep a small cushion.

My first season I was trapped with 200+ CYA and I regularly swam in 20 FC water. Eyes open underwater, even. It all depends on the FC/CYA ratio.
 
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jimbethesda

Gold Supporter
Jul 2, 2018
464
Austin, TX
Regarding the CYA test. I get the back to the sun and waist level. Is my body supposed to block the sun so the vial is shaded? Or full sun beating down?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,932
San Dimas, CA (LA County)
Regarding the CYA test. I get the back to the sun and waist level. Is my body supposed to block the sun so the vial is shaded? Or full sun beating down?
You want bright indirect light, otherwise the reflection off the surface messes with the view. I hold just the very top of the view tube with thumb and forefinger, and do it on the patio so there's lots of light reflecting off the concrete.

If you're really OCD buy the standard solution R-7065 CYA Standard 50 ppm (2 ounces)
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
Basically from my understanding the CYA test is to test how much small particulate forms when you add the binder to the CYA. Indirect light makes the light scatter when it enters, which blocks the view of the dot when you look at it.

If there’s too little indirect light, it won’t have enough light to scatter it and the dot will be visible when it should otherwise be obscured. But direct light, like direct sunshine, can make the dot too strongly visible and you can see it when you otherwise wouldn’t too.

So - strong sunny day, but back to the sun so your shadow is over the tube, but don’t hold it by wrapping your hand around the tube and blocking the indirect light.
 

Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
908
Verona, MO
Instead of looking at tube while adding the mix, I like to add to 100 level, lower and glance at the dot. If I see it add to next line, glance again. Do this until you can’t see dot.

You can pour the mix back into bottle, shake and do this multiple times to get an average if you wish.
 
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