CYA Testing Procedures

[New2Me]

Every time I took a sample in for testing the CYA numbers didn't match mine, and I was concerned because they used a Taylor K-0203 Counter Lab Rx1($705). I was using my cheapo HTH test, so I decided that I needed a better one, and purchased Taylor R-0013-E($8.80), 4088($9.45) slide comparator and a 9193 ($2.25)tube comparator( I think that is what is included in the TF-100). I found the online directions for the 9193 tube usage, but had to call Taylor for the 4088(it is part of the K-0203 Counter Lab, which is really why I wanted it.) The 4088 test instructions say to lift the rod to mix for 30 seconds, wait at least 2 minutes, then read before 5 minutes, where the tube instructions don't mention waiting at all. I took a sample, tested using the 4088 procedure and got the same results from all three comparators. The 4088 uses ~20 ml of R-0013 vs. 7ml for the HTH(which I think is a Taylor 9137) and 9193, and is just a little easier to use. To read the 4088 you lower the rod until the dot disappears, instead of pouring in the sample. From what I can remember of the last PS test, they didn't mix for 30 seconds, and they certainly didn't wait for 2 minutes, so I think that is where the difference is occurring. Inexpensive equipment used correctly is MUCH better than costly equipment used incorrectly! Of course, now I don't need them to test it for me

 

[TomU]

The instructions for the 9193 and the 9197 say to mix for 30 seconds and then slowly transfer cloudy solution to view tube. Did you notice any difference between reading immediately after mixing and reading 2 minutes later? I would think if the two minute wait was important, they would tell you to do it with all variations of the test. I've always wondered if the air bubbles in the water from shaking were affecting the results. How vigorously did you pump the lever up and down in the 4088 tube? I also wonder what happens after 5 minutes...does it become clear again or more cloudy? I'll have to try this when I get home. Did you feel that with the larger tube (and volume of fluid) that you could be more precise (and repeatable)? Thanks for sharing your findings!

 

[Guest]

When using the view tubes you should shake the dispensing bottle for 30 seconds, then let it sit for 2-5 minutes (I do this as the first test then do my other tests before reading CYA), and then give it a quick shake to disperse the precipitate and dispense into the view tube. This insures that all the CYA and reagent have reacted, particulalrly if the water is on the cooler side. The precipitation reaction is NOt instantaneous but does take a bit of time to complete. Also be aware that very high water temps can cause this test to read a bit low.

The larger view tube uses more reagent per test but it is easier to read. In theory the 4088 is a pit more precies than the large view tube but for the additional amount of reagent needed I don't feel it's really worth it for the home user. It does have benefit in a store because it does make testing a bit faster if done properly.

 

[TomU]

Waterbear,

From your description, it sounds as though you can do things to make the test read low, but it is unlikely that the test will read high. Is this correct?

 

[Guest]

Waterbear,

From your description, it sounds as though you can do things to make the test read low, but it is unlikely that the test will read high. Is this correct?

Not necessarily. If there is any cloudiness to the water itself (such as from algae or calcium carbonate precipitation or use of a phosphate remover) then the test will read higher than the CYA level.

 

[New2Me]

I was getting MUCH higher readings than the PS, thats why I was trying to find out where the differences could come from. I tested with the small tubes, not waiting the 2 minutes, and could not tell much difference from when I did wait(it probably takes me more than two minutes to fill and look, add a little more, look again, etc..). When I used the 4088, I pumped the rod fairly fast, about the same as I shook the 14 ml sample bottle. The water temp is in the 80's. The big advantage of the 4088 is that you drop/lift the rod until the dot disappears, and don't slowly add more sample. The disadvantage is that you need to hold the rod steady when the dot goes, and you take the reading(I'm very nearsighted ) I also had a time keeping the sample bottle for the small tubes from adding too much(its a cheap bottle that leaks too) If you don't do the agitation, you don't get complete mixing,and the result will be lower readings. That is what is happening at the PS, they added water to line A, R-0013 to line B, and then took a reading, no stroking! The 4088 also has an upper reading of 100, so if the CYA level is greater than that, you'll still be left guessing! Some one smarter than me can probably tell us if there is batter accuracy, or precision, in using a 20 ml sample vs. a 7 ml one.

 

[MikeInTN]

Cold reagent will also cause the reading to be high. I found this out from previously storing my reagents in the refrigerator. After letting them come to room temp, my CYA readings dropped by 20 consistently across three different samples, and also when using fresh reagent.