What's the most accurate CYA test?

After looking at the Best Guess chart and chemgeek's charts, it seems that I should keep my CYA at around 20 so I don't need to have FC above 3 or 4. Because of a slow leak, I do lose CYA over time, so I've been alternating using bleach and trichlor, depending on my CYA level.

What's the best CYA test out there? I have a Taylor kit with the "little black dot" test, but this seems highly subjective. Also, the results can vary depending on the amount of ambient light, direction of the light, etc. Plus 20ppm is at the very limit of the test's scale. I also bought an AquaChem strip test, but its results are more like rough estimates than anything else.

Are there any better tests out there for CYA?

short of buying a turbidity meter the disappearing dot test is the best one out there. Why do you want to keep your CYA so low. You might find that you get better results keeping it between 30 and 50 ppm and keeping your FC at 3-4 ppm.

Well, I'm basing the 20ppm on the chart here: http://www.poolforum.com/pf2/showthread.php?t=4236 At 30-50ppm, it looks like I'd need FC of 4-6ppm. I guess that's not a huge difference, but I'd like to keep my chlorine level as low as possible.

As for the test, are there any specific guidelines on the conditions under which to perform it? Do they assume you're testing outside? Should the beaker be in direct sunlight? I get a big difference in results depending on whether the sun is overhead or is low in the sky. (Light shining through the side of the beaker makes the dot more visible.)

I don't know... that test just seems goofy to me. I can't believe someone hasn't come up with a better way. The CYA strip test changes color. You'd think that someone could make a dropwise color test for CYA. :confused:

The method I outline in this thread below should help you to be consistent in your CYA testing. Because the test is so subjective it may be tedious to some people, but if you want reliability in your testing you have to be consistent.

Accuracy of the CYA test will always be debatable, but until you are consistent with the way you test, this will be the closest to accuracy that you can get.

Pat

http://www.poolforum.com/pf2/showthread.php?t=1855

Thanks, Pat. There's some very helpful information on that thread.

does anyone else have the plastic type tube with the dot in it? i thought that is what everyone has..it's called a taylor C.A. view tube and the range is from 20 to 100. it's what i was given when i bought my pint of test re-agent this summer. seems to work quite well

dafletcha,

Don't forget that part of the reason for having higher CYA with higher chlorine levels is to have enough in "reserve" so you don't go below the minimums at any time during the day. If your pool is exposed to sunlight, then it may lose around half of it's total chlorine in a day assuming you have at least 30 ppm of CYA (it will lose even more with less CYA). If you have a pool cover, then you can probably have low CYA and low chlorine levels, but without a cover and with exposure to sunlight, you might not be able to do it.

See what your chlorine loss is during the day and specifically between the times you pour more chlorine into your pool. If you think you can keep a minimum level, then fine, but if not, then it's better to play it safe with higher CYA and higher chlorine. That's why Ben's chart doesn't "roll off" to very low FC at low CYA because it's really hard to maintain very low FC in outdoor pools exposed to sunlight.

Richard