CYA test is pretty subjective, isn't it?

[BillyBumbler]

You know, this test has me pretty confused, I've gotten quite good at all the others except for this one. There is a point where the black dot almost dissapears, but you can still barely see the outline of it. From there to where it is completely gone is quite a spread, like 20-30ppm. So I'm not sure whether I am at 60-70ppm or more like 30-40ppm, and it makes quite a difference in how much FC I should maintain. How should I judge this test?

[cwstnsko]

Yes, it is quite subjective. I find it helps to place the dot over a light background. When I think the dot's gone, I check the reading, then add some more liquid to see if it "goes away" even more. If it does, I take another reading

[PatL34]

This test is very subjective. So much so that I have had to remove the subjectivity as much as possible.

My method is painstaking, literally, but is as follows:

1. Clean the tube that has the spot with bleach before EVERY test.

2. Follow the instructions for adding the sample and CYA. Wait at least a minute before the next part. Shake the mixture thoroughly to get the best reading.

3. Go to a north facing window. Check the point at which the black dot appears or disappears, depending on the equipment and test procedure. Make sure that your fingers are not covering any part of the tube.

4. As soon as the dot appears or disappears, that is your reading. Do not try and find another reading if you don't trust your eyesight. If you don't trust your eyesight, find someone who can. I am not being sarcastic here, just trying to make sure the test is being done correctly.

This test is difficult enough without being consistent, but as Ben says it is the most subjective test you will do in checking for CYA.

Hope this helps.

Pat

[waterbear]

Ditto to what PatL34 said!

[vanhout]

What do you considered "disappeared"? Is that when it's gone when you casually look at it, or when you really strain to see it? That's the part that always gets me...

[cygnusecks]

So, is this the best the industry can come up with? Surely there are more accurate ways of detecting, and I'm sure there are some people (including me) who might pay more for the test, given that it doesn't have to be done very often. Do the pool pros guess like this?

[geoeremite]

What do you considered "disappeared"?

This is the question I still wonder about. Which of the following have "just disappeared"? (Click on the photo to get a larger copy.}


Empty, 50, 40, 30, 20

What do you think?

cheers,
Scott

(I'll leave the picture up as reference if we come to consensus.}