Falling CYA

[fredricr1]

After a very rainy winter in southern California, my CYA was low. In Feb I brought it up to 70 (I try to keep it between 70-80) but noticed difficulty keeping up with FC loss on my usual SWG settings and was having to run it at a setting of 80%. Checked CYA about 3 weeks ago and it had dropped to around 50-60 (sorry for lack of precision - you all know how subjective that test is!) so I added another 1.5 pounds of stabilizer and the next day it was up to about 80. Cool. Because FC had dropped kind of low to about 3, I didn't SLAM but brought it up to about 13 or so and brushed the heck out of it. CC was negligible so I felt I was fine. After 4 days of sunshine (and the SWG running about 15% of the time to let the FC drift down slowly) I measured today and didn't get ANY reading of FC using the Taylor FAS-DPD test. No color change after the 5 drops. Last year it seemed to take a week or more to bring FC down from the teens to about 5 or 6. Checked CYA again and it is around 60-70. Not extremely low, by any stretch, but still lower than 3 weeks prior.

Any idea why CYA would be dropping this much despite no rain? As I'm typing this I could turn off the auto-fill valve and see if I have some kind of strange leak in this 2 year old pool, but otherwise...? Or any other idea why FC might fall so much faster than it did last season or the season before? Weather is largely the same - San Diego is pretty consistent that way.

I hope the above made sense - I tried to be thorough! TIA.

 

[Mdragger88]

U need to do Overnight Chlorine Loss Test - it looks like a SLAM Process may be in your future if you’re having large fc loss.
For the test when you added dpd powder the sample should have changed color if chlorine was present - did u forget to add the powder or are you referring to the oto total chlorine test?

 

[duraleigh]

I think OP is referring to OTO test, also.

Regardless, the OCLT should be done this evening......it certainly appears there are organics in your pool consuming chlorine.......not CYA.

 

[fredricr1]

I think OP is referring to OTO test, also.

Regardless, the OCLT should be done this evening......it certainly appears there are organics in your pool consuming chlorine.......not CYA.

Definitely meant FAS-DPD test from the K-2006. I know I put the powder in - I checked and there were still a few granules on the bottom. I'm very willing to consider I may have made a mistake somewhere, but I had pool water, powder, and as far as I know, used the correct bottle of R-0871 drops (honestly...I've never grabbed the wrong bottle from the kit before but perhaps???). I actually started a SLAM yesterday to be safe but the CYA issue was odd, prompting my post.

I admit my SLAM procedure has started out sloppy. I put in 4 gallons of 6% bleach which was almost exactly what the Pool Math calculator said. I also ran my SWG for a few hours at 100% to get it up higher. Couldn't test until 9pm and FC was 21 (shooting for 28, per Pool Math). I kept the SWG on overnight to try and raise it some more. Just tested this morning and TC was 18 - going in the opposite direction (and yes, I cannot do an OCLT test with the SWG on - I was just confirming that I am reaching my target). Clearly I'm burning chlorine. BUT...the CC test was .5 (cleared after 1 drop). Water is crystal clear. I get that the CYA isn't a factor over night so I'm going to continue with a proper SLAM but still not sure why my CYA appears to be decreasing.