CYA test is pretty subjective, isn't it?

[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.

[Lenny]

As the title of Ben's "best guess" chart implies, this isn't an exact science so there wouldn't be much point in worrying about perfection with this test.

So far, I've been able to get consistent readings as long as I test in similar light conditions. If I run into algae problems, I'll run the chloring levels a bit higher. No biggie.

[waterbear]

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...

The HAVE devices like that...they are called digital pH meters, ORP meters, Colorimeters, turbudity meters, and conductivity meters (and possibly some others). Good ones can set you back thousands of dollars. The also require standard solutions to calibrate them and some of the electrodes needs special care such as being stored wet. They are actually more work and more time consuming in the long run and won't really give you much benifit over a drop test. You don't NEED that level of accuracy to maintain your pool!

Reagents do go bad, Strips have very little precision, but electrodes go bad and batteries get weak also and if a meter is not properly calibrated (pH meters are a horror to calibrate!) then the test results won't even be as accurate as a strip! I have worked with several of these types of electronic testers over the years in laboratory settings, as an aqaurist, and as a 'pool store guy'. I use a drop based kit for my own pool and my water is perfect.

[CarlD]

Those pictures are great! But only as an example. I would NEVER estimate the CYA level based on them. Cameras pick up things the eye doesn't and may be making the CYA look lower than it is.

I have outdoor speakers on my deck. No matter HOW I look at them I cannot see the woofer and tweeter through the grill. But the pictures taken CLEARLY show them... That's an example of my point. The camera is a better "eye" than the eye.

[geoeremite]

I was with MikeK; when I took the pics I thought it might be lower than 20. But that's probably interpreting "the center is no longer darker than the outside" rather than the black dot "just disappear".

Interestingly (well, for photo geeks), these pictures overestimate the actual readings due to a combination of two factors: (a) they were taken very close to the top of the vial rather than from a distance (i.e., not waist high), (b) the small depth of field of cameras in general, but particularly at this small distance, causes the cloudiness to have a greater effect in the picture than in person. Indeed, although I can hardly see any variation in brightness in the 20 ppm picture, I could see definite variation in person.

Scott

[BillyBumbler]

Well, one thing that helped my original predicament. There wasn't much difference in appearance of the dot from 80ppm to 50ppm. So what I did was to test a new sample made up of 50% pool water and 50% tap water to dilute the sample and see how it went. Well this time it was much easier to read and the result seemed pretty conclusive at 40ppm (which unfortuneatly means that I am at 80ppm, too high). Anyway perhaps higher CYA numbers are harder to read than lower?