OCLT...scratching my head...

EricJ320

Active member
Mar 27, 2020
30
Tennessee
Pool Size
23000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
I’ve been slowly stepping my CYA up, when I did my FC had shot up to around 12 and was staying there pretty consistently. I was leaving on a 4 day trip out of town, and before I left I moved my SWG down one setting to 25% and reduced the time by 2 or 3 hours with the intent to bring it down while I was gone. Upon return my FC was at 7, but my CC came up to 1, from 0 most times, sometimes 0.5. Even though my FC was at the high end for my current CYA level I was concerned I had something going on, pollen is very bad for us this time of year, I thought perhaps that was the culprit. So I did an OCLT, now this morning it was FC 8 and CC 0.5? I even retested this morning, exact same results.

I can’t explain it. SWG and pump were both off the whole time. The pool is crystal clear. I’ve been drop testing with a K-2006 for over a year and I feel pretty confident in my technique. I’ve watched all the videos, taken all your advice, vertical bottle, don’t rush the test, don’t squeeze the bottle, let the drop develop and gravity take the drop, using a speed stir, I can consistently recreate each test (except that awful CYA test). I’m at a loss, I’m now less concerned I have an algae outbreak, but I would like to know what I’m clearly doing wrong. At least I thought I knew enough to know the OCLT shouldn’t increase my FC level. Any suggestions?

Perhaps not running the pump overnight developed a localized FC difference in samples from last night to today? Not enough pump run time after my SWG shuts down for the night to properly mix the last bit of FC? I’m struggling to find any changed variables.
 

CrystalRiver

Well-known member
Jun 19, 2020
532
Massachusetts
Every test, including FC, has a margin of error. 7 vs 8 is within that margin of error.

For the future, you should run the pump for at least 30 minutes before collecting any water samples. I don't think that mattered here, as you were looking to see that your FC did not drop, and that was confirmed.
 
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EricJ320

Active member
Mar 27, 2020
30
Tennessee
Pool Size
23000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
Every test, including FC, has a margin of error. 7 vs 8 is within that margin of error.

For the future, you should run the pump for at least 30 minutes before collecting any water samples. I don't think that mattered here, as you were looking to see that your FC did not drop, and that was confirmed.
Thanks, I hadn’t even considered margin of error. Sounds likely to be it. Also, I’ll be sure to run the pump before collecting samples. I’d add, I normally do, today just happened to be me trying to beat the sun to the pool for the OCLT, I guess I beat my pump schedule as well.
Thanks again!