Getting inconsistent fas/dpd results.

[punkbuddy89]

I'm still getting the hang of doing the test with the tf test kit. I've learned how to get consistent drop sizes with the reagent. And I use enough dpd powder. And I use 5 drops of r0003 to test for CC. But here's the situation I'm having now.

Tested the water this morning and got FC - 3.5. CC - 1. TC - 4.5

Tested two more times immediately after the first test and both times got, FC - 4.5. CC - 0. TC - 4.5.

It has been like this since I started testing this year. What am I doing wrong? Is it possible the the r0003 is remaining in the graduated cylinder from the first test and causing me to effectively test for the TC in subsequent tests?

I also just got a speed stir so I don't imagine that I'm swirling the test wrong since it's done automatically now.


Thanks for any input you all have!!

 

[JasonLion]

There are two things I can think of that could cause that. The first is taking too long when doing the test. CC can "leak" into the FC portion of the test if you take too long. However you would need to be going rather slowly for that to happen. Second, are you sure the sample is turning completely clear? Towards the end of the FC portion of the test the sample can be a very pale pink that doesn't show up well. If you miss that pale pink and continue on to the CC portion of the test, some of the FC reading will be read as CC.

 

[bridgman]

If you're not rinsing the cylinder out thoroughly with tap water *after* the test and rinsing with a bit of sampled pool water at the start of the next test give that a try.