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?

[PatL34]

I am certain the "pool pros" as you call them are nowhere near as thorough as I am. They do not clean the tube with the spot enough times to give any sort accuracy or even consistency. The store where I go to for the occasional water analysis does not clean the tube, even when I ask them to.

That is why I do it myself.

Pat

[waterbear]

The alternative is to use a turbidity meter or colorimeter. some pool stores use them. some use the melamine reagent and the disappering dot. Meters are expensive (good ones in the range of about $600 and up) and do need to be calibarated. If the test is done properly it can be as accurate as a meter (almost). Where I work uses the LaMotte Waterlink Express meter to test (it uses little plastic tubes with a measured amount of reagent in them [Unit Dose Vials] and 3 ml of water is added for the test. They are thrown away, tube and all after each individual test. The meter is calibrated with a blank before each battery of tests) and I get identical results at home with :
1 Ben's ps234s
2 Taylor K-2005
3 Walmart Aqauchem 'cheapie' kit
(as a side note test strips always give me a lower reading)

Another pool store in town uses Taylor's water lab and the cya results depend on who is doing the test. When the owner does it it matches. when the young girl does it it is ususally low (prime example of bad testing procedure, i guess)

The way I do the test at home is as follows:
The first test I do is CYA and I read it about 3-5 minutes after I do it. I start doing other testing in the meantime, usually my FC, TC and maybe pH.
the procedure I use is:
1. make sure the pool water sample is at room temperature (70-80 deg.) before I start because cold temps will slow down the reaction and can give you a low reading because of incomplete precipitation and I have read that high temps (above 80 deg.) can also have adverse effects on the reading (don't exactly know what but possibly allowing some of the precipitate to dissolve and also give a low reading) and then mix pool water sample and reagent in bottle and shake for 30 seconds.
2. let bottle sit for a few minutes and continue with other water testing.
3. make sure I read CYA test before 5 minutes from time of shaking has elapsed. (don't know how important this is but I have read that the test should be completed within 3-5 minutes from different sources)
4. before transferring to CYA tube shake bottle hard for 10-20 seconds.
5 .VERY SLOWLY (almost a drop at a time) transfer solution to tube either with northern window light or outside in shade. Tube is at waist level.
6. read results when black dot seems to completely dissappear.
7. If I want to check my results I pour solution out of tube back into mixing bottle and repeat test. (this is a good way to learn if you are having trouble reading it.
8. wash tube and bottle out carefully and completely so no residue is left in tube

I am the first to admit that I am anal about my water testing! but if you are having problems then perhaps you might want to try something similar to this.

[cygnusecks]

Thanks for all the great responses. Ever since deciding to build the pool I've hoped for a digital chemical reader, where I dip it in the water, and it instantly gives me a digital readout of all chem levels, and/or tells me exactly how much of what to add to bring the water into balance. I wonder what such a device would cost or if it's possible to build!

I grew up with my pool owner friends' parents always doing the "strips" or the dropper test, and always felt it very subjective. What if you're color blind, or what if your strips are bad, etc...

[CarlD]

The CYA test takes practice to get right. You should try to always do it the same way, everytime.

The nice thing about the test is you can run it several times in a row--just empty the test tube back into the squeeze bottle and do it again. No need to use more reagents!

I hold it at waist level, facing the sun. I add the liquid, slowly (DUH!!!!!) and see when it looks like the dot is disappearing. I move the tube back and forth a little to see if I can see the dot, and add more from the squeeze bottle until I cannot.

Then remember that if you are NOT on a line, the scale is logarythmic, not even. So halfway between 30 and 40 is NOT 35, but more like 33, and 3/4 of the way to 40 is more like 35.

Again, though, do it the same way everytime.