CYA testing

[Chaddy]

I just received some new R0013 and some 50 ppm standard solution. I guess my eyes must be too good because I tried it out twice and got 35 and 40 ppm. I was even stopping while I felt that I could still see the dot. If I am getting these results for the standard solution then should I assume that my CYA is 10-15 ppm higher than I had previously thought?

 

[jblizzle]

How are you doing the test? Try to find light that produces the correct 50ppm for the standard.

 

[steveg_nh]

I worry about this too, that different light brightness is affecting my reading. I don't have the standard 50ppm solution to compare my lighting with.

 

[BoDarville]

I would suggest taking a gander at these Extended Test Kit Directions. The CYA test is covered in post #8. The lighting is indeed critical to this test.

 

[Patrick_B]

Good suggestion Bo, +1

 

[Chaddy]

Right. I have done it exactly as instructed. I've even taken it around in different types of light. Indoors certainly gives a different view than outside with your back to the sun, but even then I get low readings. I even asked my son to take a look. Obviously it is the most difficult test, but it is also an important one.

 

[Chaddy]

Just an update on this, as I have not been checking for a while. I am obviously a novice at this but I found that the right light is definitely key. I needed bright, clear, midday sun to get a decent reading. Clouds or afternoon sun were no good. Even in the right conditions I felt like I could faintly see the black dot through the test solution at the 50ppm fill line. However, now that I have that as a frame of reference to compare to I feel like I know what my CYA is.

 

[steveg_nh]

I actually found that when I was doing it, what I thought was the black dot, was actually the reflection of my head in the liquid! lol.

 

[wayner]

For any experts reading this thread - what is the margin of error for this test? Given Chaddy's experience it would be about 15 ppm at the 50pm level. At higher levls, like in the 70s, then the margin must be even higher since a 10-15ppm error in the 50s equates to more like a 20-30ppm error given the nonlinearity in the test cylinder - see the photo below for the scale.

Is there no way to come up with a better test?

 

[RobbieH]

You can get the larger test kit from TFTestkits.net that will allow for smaller error based on larger tube and amount of reagents.

This video may help with your test method:
https://www.youtube.com/watch?v=NxaqoW-_MCs&list=UUNFkPFCkt9Y_YYNAeLtUr1g

 

[wayner]

Looking at that test tube it doesn't seem like there is a huge difference from the Taylor - there still is just a couple of mm between 60 and 70 which is the relevant range when you have a SWCG. The one you are talking about is in the photo below, correct?

 

[RobbieH]

The one I use is not like any of those. I'm on a conference call at the moment, but once I am off this call I will get a picture of the difference. I think I still have my small tube also. My mix bottle is double that size too.

CORRECTION: When I looked at the picture, I thought you had the small tube like on the left in my picture, but you already have the large one.

Ignore my creative smudging, I am a stickler for privacy and wasn't sure what might show up in my background.

 

[jblizzle]

I have the larger tube with the black lines from the TF-100. What I do is run the test normally, pouring back and forth a few times to measure in the 70-80ppm range. Then I dump half the solution and add back in tap water and repeat the test and confirm that I read in the 35-40ppm range.

Last weekend I tested a little low it seemed around 60ppm, diluted and got about 30ppm ... so that seemed to validate the first reading.