CYA test with Hach DR/850 Colorimeter

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H

hamop78

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LifeTime Supporter
Mar 29, 2007
18
Central PA USA
As everyone knows the CYA test in the Taylor kits leaves a lot to be desired. Recently I found a Hach DR/850 Colorimeter ($20.00 at a public auction --- Local lab went belly up) . I bought the appropriate reagent from Hach ($17.00 for 50 powder pillows) and ran my first test using both methods. I was amazed at the differences in the results.

I have both the Taylor kit and the Rainbow lifeguard, both showed <20 PPM but the Hach colorimeter result was 35 PPM. I ran a standard using the method in the Hach procedure manual and zeroed the instrument.

Which result should I believe.

This instrument is way over kill for the pool but I wonder what other tests (Pool related) it might be good for.
 
The Hach Colorimeter claims that it can measure CYA from 7 to 55 and is +-1.2 at 25. They don't mention this, but they would obviously be less precise near the ends of the range. The Taylor test measures CYA from 20 to 100 and is +-10 through most of that range, though novice users are often more like +-15 or even +-20 because of difficulty in interpreting the test results. Palintest makes meters that claim a test range for CYA of 0 to 200, though they don't appear to make a precision claim.

The range on the Hach test is rather narrow. Also, colorimeters typically have trouble with turbidity tests and I find their precision claim difficult to believe. The ColorQ is based on similar technology and it is far less precise than the Taylor test.
 
The LaMotte waterlink express colorimeter has a range of 0 to 150 ppm with an accuracy of +10/-25 ppm. My experience with this unit is that it consistantly measures low compared to the Taylor test. I tend to beleve the Taylor test.
 
Thanks for the input

The accuracy range of meter is where I like to keep my pool 25-35 so I'll do some further testing to see how it goes.

None of the pool stores in the area can produce acceptable results and have even detected up to 20 ppm in a sample of distilled water I took them :twisted:

I have reagents for 50 tests so.......could be an Ebay item in the future. I'm certain I can get my 20 bucks back.
 
The ColorQ CYA testing on my unit is just as bad as the Pool Store reading. Weekly, I test using the ColorQ vs TF100. Friday's CYA reading on the ColorQ was 6 and TF100 was 40. The week prior I took samples to two differant pool stores and my CYA was about 50 on average. (Both store reading where off...)
 
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