CYA drop tests are somewhat subjective...

[psteichen]

Hi, another new pool owner. I ordered the TF100 test kit and tried it out today on CYA. I agree with other posters that it is very difficult to tell when the dot disappears. I put in the recommended amount of CYA to bring my freshly filled pool up to a CYA level of 40. In doing the test the dot mostly disappears at around 40, but really if you look very carefully you can see it ever so slightly even when the tube is completely full. I'm not sure how this subjective decision as to when the dot disappears is any more accurate than the subjective decision as to what color the test strips are. It appears that different lighting levels greatly affect the results, as does asking different people to read it. My wife sees it disappear completely at around 40, yet if she hands it to me I can see the dot.

I wonder if someone could make a little blacked out tube with an LED in the bottom, and a light sensor in the cap that would give precise light transmission readings based on how occluded the solution is. This could be calibrated before testing to adjust for differences in LED light output due to battery drain or aging of the electronics by using a calibration solution that has a known occlusion level (either premixed or mixed by the consumer as needed). I know this would take some work, but these days programmable microchips would make it pretty cheap to produce. Anyone here have more free time than me?

Am I putting too much weight on this test? Is it really not that important? Should I shoot for a higher CYA level just to be on the safe side?

In case someone wants to double check my math on the CYA I added, I added 2lb of dry 96% pure CYA to 6300 gallons of fresh well water.

Thanks for any advice.

 

[linen]

Re: The dot mostly disappears at around 40

Welcome to tfp, psteichen

Yes the cya test can be challenging. Make sure it is sunny and you stand with the sun to your back with the tube at waist level. In the extended test kit instructions there is a link to Taylor's site that has a picture of what you are looking for.

The test is important since it tells you how much FC you should be maintaining.

In case someone wants to double check my math on the CYA I added, I added 2lb of dry 96% pure CYA to 6300 gallons of fresh well water.

That should have got you to about 40 ppm cya if you are sure you started at 0 (didn't add any or use trichlor or dichlor).

How did you add it?

It can take up to a week for granular cya to show up in test.

 

[Butterfly]

Re: The dot mostly disappears at around 40

Yep, you got about 40 CYA in there

Did you

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.

Here's a link to Extended Test Kit Instructions.
It includes a link to Taylor w/visuals on the test procedure: extended-test-kit-directions-t25081.html

Here's a link to the TFTestKit.net CYA video: http://www.youtube.com/watch?v=NxaqoW-_MCs

 

[Durk]

Re: The dot mostly disappears at around 40

Dave (TFT) also sells a 50ppm CYA Standard solution for $8.95. You can use that to calibrate your technique, as it were. I think it's a great way for a beginner to gain confidence in their technique. I wish I had known about it when I first started doing my own CYA tests many moons ago.

http://tftestkits.net/R-7065-CYA-Standard-Solution-p34.html

He also has them for TA and CH.

 

[Isaac-1]

Re: The dot mostly disappears at around 40

I find a lot of times what I am seeing is the reflection of the top of the tube thinking it is the black dot when the dot has in fact vanished. As to the strip test, the big problem with most of them is the scale for the color range when your choices are 0, 75, 125 and 175 or some such, 3 of the 4 readings are above the suggested range, which makes it very hard to tell where you are inbetween the first 2 shades.

 

[psteichen]

Re: The dot mostly disappears at around 40

...Make sure it is sunny and you stand with the sun to your back with the tube at waist level.

...That should have got you to about 40 ppm cya if you are sure you started at 0 (didn't add any or use trichlor or dichlor).

...How did you add it?

It can take up to a week for granular cya to show up in test.

Well, there hasn't been full sun here since I put up the pool, but I did try to use bright house lighting. Your point about needing to wait 1 week before testing may be an issue. I added the granular CYA 4 days ago by dissolving it in water and then poured in slowly in front of the return jet. I'll try the test again in a few more days.

But the fact that this test is somewhat subjective is still disappointing. I wish I had known to order the 50ppm test fluid with my kit. Now I'd have to pay shipping again.

Thanks for the ideas everyone!

 

[jblizzle]

Re: CYA drop tests are very subjective...

All the other tests give the sense of a required accuracy ... in reality, there is no need to be that exact. The CYA test at best is +/- 15ppm ... just pour the sample back and forth a few times and see if you consistently get a similar result ... then don't sweat it and trust that.

Try doing the test with the same sample in varying light conditions and you will see if/how it impacts the result.