OCLT question

[oupunk]

I am trying to close my pool and have been doing on OCLT for a week now. CYA=60 slam FC=24, yes? Ph=7.4, water is crystal clear. Yet, I have an overnight loss of 4-5ppm. I did 3 days of slam, vacuuming, backwashing, and each morning a 4-5ppm loss. I decided its getting cold, today was down to 28 degrees, and to stop the slam/oclt and see where FC stablized. Currently have had FC=11 for 48h without any loss. My question is: IF there is algee in the pool how is it that there is no OCL at 11, but at 24 there is? What am I doing wrong? Is it safe to close the pool if I get FC back to 24 and then just cover the pool?
TIA

 

[ajw22]

Yes, just close the pool.

An Overnight Chlorine Loss Test is best performed at a FC of 7-10 ppm. At higher FC rates there is a natural chlorine loss having nothing to do with algae.

 

[oupunk]

Yes, just close the pool.

An Overnight Chlorine Loss Test is best performed at a FC of 7-10 ppm. At higher FC rates there is a natural chlorine loss having nothing to do with algae.

thank you. Just for my understanding, I thought the OCLT was part of the SLAM and that FC during a slam is almost always higher that 10. If I test when it is dark and again in the morning before sunrise. What is causing the loss if not evap or algee? I would assume the evaporation would occur even overnight, but that is not how I read the OCLT to describe the process.

 

[ajw22]

High FC levels naturally degrade.

 

[Mdragger88]

Were you slamming because you had algae or just raising fc to close?
If it was because of algae be sure you have checked all the hiding places as that can cause a failed oclt even though the pool looks clear.
*Check & scrub every nook & cranny where algae may hide (light niches, steps, drain covers, ladder handrails, skimmer throats/weirs, etc.)

 

[oupunk]

High FC levels naturally degrade.

By how much over an 8h period with no sun? If a loss of more than 1 is considered a fail for the OCLT, then I would not have lost 4-5ppm without algae? Hypothetically let's say I do have mustard algae next spring and I slam what is an acceptable amount of loss for an OCLT if the high FC naturally breaks down?

 

[Texas Splash]

IF there is algee in the pool how is it that there is no OCL at 11, but at 24 there is?

You mentioned in Post #1 there was a 4-5 ppm loss earlier in the SLAM, but as the water temps dropped, that's also when you lowered the FC level. It's possible you had been dealing with an algae issue, but with higher water temps the FC loss was more noticeable. Now that water temps have plummeted, the algae is much less active and hence less FC loss. Other than a testing error that's my theory. If you're not losing any FC now, I would just prepare to close and open as early as possible next spring .