CYA drop?

[singerteacher]

I know this isn't supposed to happen ... but it did. I tested CYA today and it was lower than the last test. From 65 to 45ppm.

I started the summer (a new pool owner) with low CYA and lots of leftover chlorine pucks ... so I've been using them and watching my CYA slowly go up all summer. My goal was 45ppm. When I last tested it, whoa!, it was 65 so out came the pucks. Worried about that number, thinking it might be even higher, I tested again today.

Today's test (using the Taylor 2006 kit) showed 45. I didn't believe it, so I did the test again. Still 45. All my other levels are close to the last reading, we haven't done lots of splashing, and there doesn't appear to be a leak (although I will do the bucket test now).

My question: Could this be user error -- as in, my eyes aren't giving an accurate assessment of whether the black spot at the bottom disappears? Or is there variation in the test, or even in where I take my water sample from?

 

[TizMe]

The CYA test is the most difficult one in my opinion to figure out whether the black dot has actually disappeared or not. I always let the wife do that test ...... as well as the PH color test

As far as why the numbers are dropping could you post some numbers here so we can have a look. Someone who has other ideas will chime in and speak up ...

 

[CaOCl2]

The fall 1995 JSPSI Journal mentions that certain chemical species might interfere with the test. The articles's author suggests adding 1 drop of bleach to the precipitated sample to remove these interferences. A few issues later Wojtowicz suggests that the sample be treated to 10 ppm chlorine then dechlorinated prior to testing

So my question - was the water shocked before test 1 and/or test 2?

 

[singerteacher]

No, I didn't shock before either test, but I did add a little bleach between tests, which were 3 days apart. Solar cover has been off the whole time, with lots of sun, wind and swimming, which accounts for the FC loss. (Planning to shock tonight, since it's been two weeks since the last shock and FC is a little low for my taste.)

Test one Test two
FC 4.0 2.6
CC 0.2 0.0
pH 7.7 7.8
TA 140 140
CH 270 250
CYA 65 45
Temp 78 79
Sat 0.4 0.45

Also, here's what my CYA tests looked like all summer, testing nearly every week starting in June (except when I ran out of CYA reagent -- darn Taylor kit!):
35, 46, 40, 47, 50, 58, 58

Since I'm shocking tonight, I'll re-test the CYA tomorrow and post the results. :?

 

[singerteacher]

Today, CYA was 55. So it looks like it was user error! Does anyone know of an easier to read CYA test?

 

[TizMe]

Im not sure how the CYA test is done on the Taylor test kits but if its done like the one in the TF 100 test kit it can be the most difficult one to do. On the TF 100 test kits it is very hard to be pouring the solution into a tube making sure you dont pour it all over the floor yet try to determine when the black dot at the bottom disappears. I dont know of an easier way but someone else may be able to give you some advice.

 

[Swimgirl]

Im not sure how the CYA test is done on the Taylor test kits but if its done like the one in the TF 100 test kit it can be the most difficult one to do. On the TF 100 test kits it is very hard to be pouring the solution into a tube making sure you dont pour it all over the floor yet try to determine when the black dot at the bottom disappears. I dont know of an easier way but someone else may be able to give you some advice.

Didn't your TF100 come with a small sqeeze bottle to mix the CYA reagent with water in, then just sqeeze that into the tube? I never have any problem with getting the fluid into the tube while watching the black dot, although light levels, shadows, etc, can make it hard to determine when the black dot is "really" gone.

 

[TizMe]

Thats what im referrng to Swimgirl. Its a judgment call on whether or not the black dot is gone or not ...