Quote Originally Posted by Amir View Post
Ront,
If you get 29 with the correct water temp and the CYA should be 60 and 70, there is something wrong with that machine. They should not advertise CYA accuracy if you do everything right and the results are off by that much.
Amir
Please reread my post near the beginning of this thread where I posted what tech support at LaMotte said about the meter. CYA is +/- 20 ppm so your reading of 29 is within spec. It can be as high as 49 and you stated that your CYA should be around 50 ppm. When doing any kind of water testing you have to look at the precision of the test. The meter is probably more accurate than a 'disappearing dot' test any day within the limits of it's accuracy since it removes the subjective element of 'when has the dot actually disappeared?" You can have 3 people do a disappearing dot test on the same sample and they can get readings that are not even close to each other! Common testing methods for CYA as used in home test kits (and even some very expensive professional ones) are a rough guide at best and should be used as such. It's really not appropirate to say "my cya is 70 ppm" since it can be off by as much as 30 ppm with conventional testing methods. At best you really only have a ballpark figure of where it is with the types of tests included in most water test kits.
As far as the calcium hardness problem, that seems to be a limitation in LaMotte's chemistry that is used with colorimeters. We use a Waterlink Express at work that uses vials of dry reagents. The upper limit of the CH test is supposed to be about 500 ppm but if the hardness is higher than that the test will still only report about 450-500 ppm. I have spoken to LaMotte tech support on this and they suggested to titrate when I got high calcium readings with the Waterlink. Interestingly, LaMotte does offer kits that include calcium hardness titration tests also. Using a meter certainly speeds up testing but does not necessisarily REPLACE other forms of testing. You need to know the limits of the equipment and use the apporpriate test under the appropriate conditions. Don't throw the baby out with the bathwater!

Just my 2 cents! (And no, I don't have a ColorQ. I use Taylor chemistries to test my own pool! I still think the ColorQ is a viable tool in water testing when used properly.)

One final note about CYA testing. Temperature does affect the test to some degree whether you use liquid or dry reagents as does how long you let the sample stand before testing. That is why I have said in several previous posts about the Taylor test to make sure the sample is between 70-80 degrees and to let the sample stand for about 5 minutes after shaking it for 30 seconds and to shake it again to disperse the precipitate before dispensing it into the view tube. I suspect that if you let the CYA sample sit for about 3 minutes before reading it in the ColorQ you will find that your CYA readings are more in line with the Taylor one.