Can shock skew CYA test results?

[DeptOfMeteors]

Before starting SLAMming, I tested the CYA levels and got 30ppm. This squared w/what PoolMath said would happen. I just tested again and found it to be well over that! At least 40ppm! Could this be because of all those jugs of bleach I've been pouring into the skimmer? Or could this be the reason why this SLAM is taking so long?

 

[davidgriffeth]

Bleach won't increase CYA. It's more likely the CYA testing. Have a look at CYA Testing - Further Reading.

 

[gingrbredman]

I just tested again and found it to be well over that! At least 40ppm!

I don't know that 40 is that well above the 30 mark, but if it is now at 40, it would mean just a little more chlorine to keep up with SLAM levels, but not terrible.

Or could this be the reason why this SLAM is taking so long?

Adding chlorine during a SLAM would have no change to your CYA level. Salt will go up slightly, but not your CYA. It could be taking so long because not everything you are trying to kill is dead yet. Have seen quite a few SLAM stories recently that are taking longer than expected. That 1% change in chlorine level according to the SLAM chart shouldn't be the reason it is taking so long, but if you know if the CYA is 40 now, just adjust the chlorine levels to match and SLAM away!

 

[Mdragger88]

all those jugs of bleach I've been pouring into the skimmer?

Please don’t pour any chemicals in your skimmer.
Bleach/liquid chlorine is supposed to be poured into the pool very slowly infront of a running return (jet)
Brush the area well so nothing pools on the liner/fiberglass/plaster.
This article outlines how to add each chemical to your pool

Recommended Pool Chemicals

Which should I buy? TFP's recommended pool chemicals are cheap, easy, and won't unbalance your pool water.

www.troublefreepool.com

As for the cya test - if it read anywhere between 30 & 40 it counts as 40ppm anyway. Always round up if between.
The test should be done outdoors on a sunny day with your back to the sun for the most accurate results. You can pour the solution back into the squirty bottle & do the test again as many times as u need to to get an average reading u feel confident in.

 

[DeptOfMeteors]

Now that I've read those instructions on the CYA test: I decided that I had 30ppm of CYA because that's the amount at which the dot disappeared. But now it seems I really had 40ppm. But no, according to the correct interpretation of the test, I have 60ppm! So now I have to shock at 24ppm instead of just 12ppm! So where did this extra CYA come from? Should I try to lower it or just shock more?

 

[Orion7319]

Now that I've read those instructions on the CYA test: I decided that I had 30ppm of CYA because that's the amount at which the dot disappeared. But now it seems I really had 40ppm. But no, according to the correct interpretation of the test, I have 60ppm! So now I have to shock at 24ppm instead of just 12ppm! So where did this extra CYA come from? Should I try to lower it or just shock more?

What????? How are you figuring 60?

 

[DeptOfMeteors]

By pouring into the test tube up to "60", still being able to make out the dot, then pouring up to "50" and then not being able to make out the dot.

 

[Steve-D]

The CYA test is a tough one...very subjective unlike the drop tests. this is my 5th year with a pool of one kind or another and only this season have I grown confident that I'm reading the CYA test correctly. Are you certain that the difference in your results isn't a matter of not consistently reading the test correctly? Unless you recently added CYA and its only now mixed thoroughly enough to show in the test the difference is more likely to be a testing error than it is an increase in actual CYA.

Did you check out the "CYA Testing - Further Reading" link in @davidgriffeth 's reply above? The Testing images from Taylor should be your point of reference.

 

[Orion7319]

By pouring into the test tube up to "60", still being able to make out the dot, then pouring up to "50" and then not being able to make out the dot.

Before you weren’t seeing the dot at 30. Did you add CYA? To answer your original question, I wouldn’t think the higher chlorine would affect the CYA test because it is a turbidity test. I could be wrong though, someone who knows for sure will chime in. You could purchase this sampler set if your unsure how to test CYA (it’s tricky) It would have a sample of CYA at a known value (most likely 50) so you can practice the test on it so you have a reference to go by.

Standard Sampler

tftestkits.net

 

[mknauss]

I wouldn’t think the higher chlorine would affect the CYA test because it is a turbidity test. I could be wrong though, someone who knows for sure will chime in.

Adding liquid chlorine (sodium hypochlorite) to a pool will NOT raise the CYA level.

 

[Orion7319]

Adding liquid chlorine (sodium hypochlorite) to a pool will NOT raise the CYA level.

The question was would it affect the CYA TEST, like how if the chlorine is over 10 it will affect the PH test. Of course it won’t affect the actual CYA level.

 

[DeptOfMeteors]

I read that article, which is why I realize that my original test was wrong. I now know that I originally must have had 40ppm CYA but now it seems to have raised to 60ppm. I don't remember exactly how it went last week, but I would have waited a while after dispensing the CYA to conduct the test.
I don't know why people are saying it's subjective. The last stage of the test seems pretty straight forward: I can make out the dot here, but I can't make it out here. I put a 2nd set of eyes on it which confirmed my findings. To me, maybe the weakest part of the test is to make out the 7.5mL and 15mL graduations. But others don't seem to think that's much of a problem.
I can tell you something you can take to the bank: I bought 3 cylinders of Aquarius's 900g stabilizer. PoolMath recommended I put in 2.6kg to get 30ppm, so I put in about 2 and a half cylinders (which amounts to a fair bit less than 2.6kg). I did it by repeatedly dumping more into a sock, then holding it in front of a jet. All I've put in the pool since is bleach. It's the "Great Value" kind I can get at Walmart. It doesn't appear to have any additives in it.

 

[mknauss]

The question was would it affect the CYA TEST,

No.

 

[mknauss]

This was fresh water fill?

 

[Orion7319]

No.

Thank you for the clarification.

 

[Steve-D]

I read that article, which is why I realize that my original test was wrong. I now know that I originally must have had 40ppm CYA but now it seems to have raised to 60ppm. I don't remember exactly how it went last week, but I would have waited a while after dispensing the CYA to conduct the test.
I don't know why people are saying it's subjective. The last stage of the test seems pretty straight forward: I can make out the dot here, but I can't make it out here...

I described the test as subjective because to me that "End test" Taylor image still looks like the shadow of a dot [edit: and I'm sure others have made the same mistake]. In the past I probably continued to add solution thus underestimating my true CYA level which would be very bad for correctly applying min/max FC adjustments.

 

[Orion7319]

I described the test as subjective because to me that "End test" Taylor image still looks like the shadow of a dot. In the past I probably continued to add solution thus underestimating my true CYA level which would be very bad for correctly applying min/max FC adjustments.

That’s how the sampler could be useful. I only became confident in my ability to interpret the CYA test this year. Once you know for sure what the end of the test should look like, then it’s pretty easy to do, and you aren’t second guessing yourself. It’s not really subjective at all when you start to get the hang of it. It’s the most difficult test to get comfortable with doing.

Standard Sampler

tftestkits.net

 

[DeptOfMeteors]

That’s how the sampler could be useful. I only became confident in my ability to interpret the CYA test this year. Once you know for sure what the end of the test should look like, then it’s pretty easy to do, and you aren’t second guessing yourself. It’s not really subjective at all when you start to get the hang of it. It’s the most difficult test to get comfortable with doing.

Standard Sampler

tftestkits.net

I don't have a standard sampler, but it sounds like you are saying that the test ends before the dot disappears completely. Like, it's enough if it's very hazy but still visible.

This was fresh water fill?

I don't know what that means. I lowered the water quite a bit last fall, but what's there now is also tap water and rain water.

 

[Steve-D]

What is being suggested is that you do a test on a sample of water from the spigot/hose you are using to top off your pool...the "fill." It is not distilled so it's going to have its own pH level, maybe some calcium and possibly iron or other things. If the "fill" water contains too much of something that can only be corrected by draining then that's something you want to be aware of so you can plan and adjust accordingly.

 

[Orion7319]

I don't have a standard sampler, but it sounds like you are saying that the test ends before the dot disappears completely. Like, it's enough if it's very hazy but still visible.

It may or may not look a bit hazy to you. The frequently given advise on this site to do the CYA test is basically “stand in the bright sun with your back to the sun with the vial at waist height and glance at the vial”. That advice assumes everyone’s visual perceptions are the same across the board with no variations from individual to individual. For example, I have excellent night vision which means my eyes are very sensitive to bright light. When I stand in the bright sun with my back turned to it, the sun reflecting off my pool deck is enough to cause me a bit of snow blindness, and I can’t accurately make out the test. I personally have way more luck simply performing the test in the shade. If you KNOW what say 50ppm of CYA looks like to you and how it looks to you under different lighting situations, then you know what 50ppm is supposed to look like. The sampler simply teaches you what to look for.