Will SLAMming drop my CYA?

[SeaCorey]

After way too much rain and being in-and-out of town, I had developed a slight yellow issue. Checked yesterday morning, pH was 7.5 and FC was 7 (from a jug dumped in on Saturday, no time for detailed tests then), dumped in a jug and opened the chlorinator (with [4] 3" stabilized tabs in it) just a bit, from just over 1 to not quite 3.
Overnight my CYA fell:

Last night : Today

FC 24 : 20
CC 0 : 2 : D/C = didn't check
CH D/C : D/C
TA D/C : D/C

CYA 22 : <20
pH D/C : 7.5

Pool temp 84*F, masonry, cover on except when swimming.

As I've been in-and-out of town I've checked the chlorine and pH with the little kit at least 2ce a week, no huge swings in either.

Is this normal, or indicative of something (possibly a testing error, although I'm not a newbie, typically very consistent, and am now out of R-0013...)?
Thanks!

 

[jblizzle]

I would chalk that up to within the accuracy of the test and your testing methods.

 

[Kiss4aFrog]

Your CYA should only change if you evaporate water out, the cya rises due to it being higher concentration. If you add water, rain, ... then the CYA will drop due to dilution. There has been circumstances where some pools over winter manage to consume/convert the CYA and the level will drop drastically or even go to zero but in your case it's likely just a testing error.

The cholorinator is a bad idea in most cases as the tablets add CYA as they dissolve and as above the CYA stays in the pool and doesn't evaporate the way chlorine does. You need chlorine daily but the CYA keeps adding until it's a problem.

 

[SeaCorey]

Thanks for the input! That's kinda what I thought, what with the test being so subjective - but yesterday I couldn't see the dot (if barely), today it's clear as day. The R-0013 is on the way, so I'll have at it again soon.

My thought about the chlorinator, being fully aware that there's CYA in the tabs, is that 20-22 is low for CYA so best to open it up just a bit (to 3 out of 10) to work its way up slowly to around 30, especially since I'm down for a few days of testing CYA. And adding CYA powder is not quick and is a bit of a pain. Also, I SLAMmed it back in early May and had to add CYA then, then it rained like crazy here this summer (we got more rain in one hour on the last Wed in May than we usually get in all of May, and it rained for all but 3 days in July and most of August), so I'm not concerned (at the moment) about excess CYA.

Am I missing important info right now by not testing for CH and TA? I thought I read on TFP that, given a somewhat stable and appropriate pH, SLAMming was best done first then address the other factors. Jason is that to what you referred by mentioning my (potentially and admittedly dubious/lazy/sloppy?) testing methods?

 

[Isaac-1]

Were the lighting conditions the same? Proper lighting makes a big difference on reading the CYA test

 

[SeaCorey]

Wow, good point. But yes, very similar conditions, I fill a pint-ish pool store sample bottle and do the tests inside, in the kitchen. Good diffuse natural light, no artificial light, 'nighttime' test was performed around 7, so this time of year still plenty of daylight.

To fill it, from the edge, I reach with the bottle upside-down [armchair shrinks just keep it to yourselves...] elbow-deep down and out into the deep end, fill, raise out of pool, empty, and fill again. I do this in the same spot, usually with pump off but sometimes with it running, does it matter if the pump's running or not?

 

[BuckeyeChris]

It should be running for 20-30 mins before the test just make sure the water is mixed well

 

[Agent99]

There is a control sample of 50 ppm CYA known as R-7065 that you can get from tftestkits. You can use that to fine tune your CYA measuring technique. You mix the R-0013 and R-7065 and it'll be 50 ppm.