CYA Loss

[yossarian]

I seem to have lost 20 ppm of CYA over the last 2 weeks, which does not make sense. I am using the Taylor 2006 test kit and when I tested 2 weeks ago, it said my CYA was 50. Last night I tested and it said my CYA is 30. We did have a lot of rain on 2 occasions after the initial test and I needed to drain some water, but I have not otherwise refilled. In addition, I have cleaned my filter once since then, which resulted in a bit more water loss, but again, I did not refill.

I am concerned that I am not testing right, although the test kit instructions and the visual guide I saw linked here made it seem pretty self-explanatory. All I know is that I could see that black dot for a long time when I was adding the solution to the tube last night.

As a side note, I do have test strips, which I had bought earlier this year and the CYA reading off of those would indicate something a bit north of 30-50 (I think). I find it very hard to interpret the CYA reading on the strips. And I know they are not as reliable. I was just using them as a bit of a check.

I am not sure if it matters, but I have been able to keep the pH within 7.2 to 7.6, and alkalinity between 100 and 110.

 

[JasonLion]

That is curious, especially because doing the CYA test at night usually gives you higher than actual results. The test is designed to be in full sunlight with your body shading the view tube from direct sunlight. The CYA test is +-15, so that is just a bit more variation than I would expect just from the uncertainty in the test.

Test strips are remarkably unreliable for measuring CYA levels.

The rain would have lowered the CYA level just a little bit, nowhere near that much.

 

[yossarian]

It seems like a lot of loss to me as well. I added CYA this year to get near a level of 45, assuming I would use tri-chlor tabs here and there. At the time I was using strips, and barely registering any color change. I assume that there was some CYA in the pool as the prior owner's used tri-chlor tabs, but since we drain quite a bit (we live in the northeast), I was not entirely surprised to see that we might be on the low end of the CYA reading.

I guess I'll have to test again tomorrow morning.