for those deficient in sun and testing CYA

[engrav]

CYA is to be measured back turned to the sun
but often have no sun

bought a cheap Garrity 3AAA 30 lumen flashlight
seems to work well, shine it through the liquid at an angle toward the black spot
can hit 50ppm most often with the CYA standard 50ppm

 

[mikech]

I put the tube on top of my smartphone, with a known brightness on a white background, calibrated against the 50ppm sample. No shadows or reflections, works consistently for me in no sun.

Mike

 

[engrav]

I put the tube on top of my smartphone, with a known brightness on a white background, calibrated against the 50ppm sample. No shadows or reflections, works consistently for me in no sun.

nice, might try that but
I always spill water

how do you keep the water off / out of the phone?

 

[mikech]

By not spilling!

 

[chem geek]

Very clever, guys.

 

[singingpond]

This is interesting -- a uniform backlit surface under the tube sounds like a good idea, especially if calibrated. Outdoors, I often have trouble distinguishing the fading black dot at the bottom of the tube from the similar size/shape roundish image that arises from the reflection of my head at the curved top surface of the water (I'm looking down at the water, after all, in order to read the test, so it's hard to avoid the reflection problem).

 

[Shirker]

Where do you get (or how do you make) a standard 50ppm reference solution?

 

[singingpond]

You can order reference solutions for a number of the tests, from the same places that sell the test chemicals. I think tftestkits has them.

I suppose you could make up a test solution with a very carefully measured amount of water and stabilizer, but you'd have to make some estimate of your margin of error, I think.

 

[pwrstrk]

Where do you get (or how do you make) a standard 50ppm reference solution?

Dave at TFTestkits.net has it. ?

 

[JVTrain]

I wonder how placing the tube on my Speed Stir with the light on would work...

 

[mikech]

That's exactly why I thought of it. My big head was getting confused with the dot.

Mike

 

[mikech]

This is interesting -- a uniform backlit surface under the tube sounds like a good idea, especially if calibrated. Outdoors, I often have trouble distinguishing the fading black dot at the bottom of the tube from the similar size/shape roundish image that arises from the reflection of my head at the curved top surface of the water (I'm looking down at the water, after all, in order to read the test, so it's hard to avoid the reflection problem).

Whoops. Should have quoted.

 

[chem geek]

R-7064 100 ppm TA Standard Solution
R-7063 200 ppm CH Standard Solution
R-7065 50 ppm CYA Standard Solution

 

[chiefwej]

My solution was to just move to Tucson where we have sun 300+ days a year.

 

[jmastron]

The idea of using a backlit surface is interesting; I will have to try that. We have sun here usually, but for various reasons I usually end up doing the testing indoors and/or at night. There's one extra-bright recessed can in the kitchen that we (the kids and I) hover under to do the CYA test. Moving the tube around a bit helps distinguish the edges of the dot from other background/shadows, but I sometimes wonder if I'm seeing phantom dot edges because I psychologically want the CYA to be lower. It has been dropping from ~90 in early July to ~70 now (after I took over the pool and stopped using trichlor pucks) with no drain, only splashout/evaporation (and I gather evaporation doesn't in theory lower the CYA), want to make sure that's real as I'm basing FC targets on it.

My only concern is if a backlit surface is too strong, and could make the dot show up when it really is invisible under the intended testing conditions. Guess there's only one way to find out -- pour back and forth to test it a few different ways. I think I'll get some of the standard solution next time I get refills; a cheap way to confirm whether I've been doing it right.

 

[timerguy]

Evaporation actually will temporarily increase cya until the water is topped off. I've used a regular flashlight indoors several times and got the same reading as I got three hrs before using the sun at my back. When I first got my k-2006 test kit, I had called Taylor support to ask them about having to have the sun at your back when reading the test-- they said it wouldn't make any difference. Waist high is also unnecessary according to them. I know that doesn't meet the conventional wisdom here, but it's does meet my experience.

 

[mikech]

The idea of using a backlit surface is interesting; I will have to try that. We have sun here usually, but for various reasons I usually end up doing the testing indoors and/or at night. There's one extra-bright recessed can in the kitchen that we (the kids and I) hover under to do the CYA test. Moving the tube around a bit helps distinguish the edges of the dot from other background/shadows, but I sometimes wonder if I'm seeing phantom dot edges because I psychologically want the CYA to be lower. It has been dropping from ~90 in early July to ~70 now (after I took over the pool and stopped using trichlor pucks) with no drain, only splashout/evaporation (and I gather evaporation doesn't in theory lower the CYA), want to make sure that's real as I'm basing FC targets on it.

My only concern is if a backlit surface is too strong, and could make the dot show up when it really is invisible under the intended testing conditions. Guess there's only one way to find out -- pour back and forth to test it a few different ways. I think I'll get some of the standard solution next time I get refills; a cheap way to confirm whether I've been doing it right.

Having the standard solution is essential, especially if you have to re-calibrate the underlit background due to other ambient light variations.

I've only just ordered mine from Dave, (arrived today - thanks!), but I have been testing weekly and my CYA has been steady at 50ppm under outdoor light conditions, so that has been my 'standard' sample.

 

[chem geek]

Evaporation actually will temporarily increase cya until the water is topped off. I've used a regular flashlight indoors several times and got the same reading as I got three hrs before using the sun at my back. When I first got my k-2006 test kit, I had called Taylor support to ask them about having to have the sun at your back when reading the test-- they said it wouldn't make any difference. Waist high is also unnecessary according to them. I know that doesn't meet the conventional wisdom here, but it's does meet my experience.

Well my personal experience is if you hold the tube in direct sunlight (i.e. facing the sun) then the dot is much more visible and you measure a lower CYA reading than if you shade the tube. At the other extreme, if you look at the tube indoors without sufficient lighting, then the dot is less visible and you measure a higher CYA reading. This is very repeatable. Try it yourself taking a sample and reading it in different lighting to see the visibility of the black dot.

Also, when I contacted Taylor back in 2008, the following was the advice they gave me:

We suggest the northern sunlight as we do for all of our tests. Facing North will alleviate the indirect/direct sunlight debate. If you have to use the simulated source, it is recommended that it pass through the side of the view tube as opposed to being put on the bottom shining up or top shining down. No luminance levels have been recorded or experimented.

They are referring to facing North in the southern hemisphere so by doing so one is largely blocking the sun with one's body though holding up a tube for some tests (not CYA) can have sun shine through it. For CYA, one must look down into the tube so facing North implies indirect sunlight, not direct sunlight.

 

[mikech]

Ok, after testing with the 50ppm standard solution, the backlit under tube method doesn't work. Varying the screen brightness made little difference. Back to the drawing board ...

 

[timerguy]

Well my personal experience is if you hold the tube in direct sunlight (i.e. facing the sun) then the dot is much more visible and you measure a lower CYA reading than if you shade the tube. At the other extreme, if you look at the tube indoors without sufficient lighting, then the dot is less visible and you measure a higher CYA reading. This is very repeatable. Try it yourself taking a sample and reading it in different lighting to see the visibility of the black dot.

Also, when I contacted Taylor back in 2008, the following was the advice they gave me:



They are referring to facing North in the southern hemisphere so by doing so one is largely blocking the sun with one's body though holding up a tube for some tests (not CYA) can have sun shine through it. For CYA, one must look down into the tube so facing North implies indirect sunlight, not direct sunlight.

Well, using multiple ways of holding the tube while dropping the test solution is exactly what I've done many times. When using a flashlight indoors, I've always pointed it through the side of the tube just like they told me to do also. Invariably, my results have been exactly the same as when I've had the sun to my back. North is North whether you're in the southern hemisphere or northern hemisphere. Here in SC, Facing North it's often hard to not have any sun directly on the tube. So, when I do the test out in the sun, I always am shading the tube with my body