OCLT affected by cold air/warm water?

capricatunes

Bronze Supporter
Jun 3, 2020
28
Minneapolis
FC: 15.5
CC: .5
CYA: 40
Ph: 8.0
TA: not recently measured

I’ve been in SLAM mode for four days (Keeping FC 16-17ppm).

The reason: The pool hadn’t been swam in for a week. Yellow/brown sediment on the bottom, but not the sides. I believe it was pollen (based on forum posts I read here). I scrubbed and SLAMMed and it was crystal within a day.

But, I’m still losing 2ppm in OCLT (Been doing OCLT since day one of SLAM). So two newbie questions:

Air temp is 46 low, 59 high - getting a freakish cold spell. Water temp is 85 😎😬 Will the evaporation cause chlorine loss? Could that be the culprit? For example, after sundown my FC was 15.5. I added 50oz of 12.5%, and three hours later the FC was still 15.5.

2) Would frogs hanging out in the skimmer overnight cause that kind of loss?

I understand chlorine is consumed by sunlight and organics. I feel like an idiot even writing this question, but do frogs count as organics? 😆

I’m at a loss as to why I’m still failing OCLT after four days - that’s never happened before. The only new variable here is air temp.

Thanks much!
 

Dirk

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Frogs and their waste count, so yes, organic. Though I would not think they alone would cause that kind of loss. Water temp is still quite warm, so you could still have algae. If you can't pass the OCLT, you've got to keep SLAMing. If all the visible signs of algae are gone, then you go hunting for it. Behind light fixtures, inside ladders, under drain covers, inside the skimmer, behind the weir door, etc.

When you say evaporation, are you actually losing water in the pool? Do you see it go down?

Have you checked the date code on your chlorine? If it is old, that could account for odd test results, but not for the OCLT result. Unless you're doing the OCLT wrong. If you're testing, then dosing with chlorine, and counting the expected result of the dosing as your beginning OCLT number, that's not going to work, especially if your chlorine is old. You test, without adding anything after, and that is your beginning OCLT number.

Keep SLAMing until you can pass the three criteria, or at least until someone else here can offer another idea. Otherwise, you risk having to start over again.
 

Dirk

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Rule of thumb: Its only pollen if you also see it all over *outside* of the pool.
Maddie, that was the dead algae, right? And if he had that much algae, then four days of SLAM might be just the first half (or less)... And maybe wouldn't that kind of FC loss after just four days still be considered normal for the SLAM process?

And capricatunes, what did you mean by "that’s never happened before?" How many times have you had to SLAM? And how many days, months, years apart?

How often are you testing? And how many times a day is the FC dropping well below SLAM level.

The reason I ask: you should never have to SLAM your pool if you're following TFP protocols carefully. I never have had to.

And every time you let FC drop below SLAM level you lengthen the time the SLAM will take. If you're losing that much FC in just a few hours, you have to test and dose (MAINTAIN) even more often.
 
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Dirk

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OK, had to ask, I've never had either on the bottom of my pool. Did we ever answer capricatunes question? I've never read here that the SLAM process, or the end-of-slam criteria were affected by cold air temp. Anything to that, Maddie?
 
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mknauss

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Water or air temperature will not effect an OCLT process or FC testing.
 
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capricatunes

Bronze Supporter
Jun 3, 2020
28
Minneapolis
Thanks for responses so far. My replies, and update below (Still failing OCLT).

Rule of thumb: Its only pollen if you also see it all over *outside* of the pool.

Yeah, we're having a lot of pollen here, so that might be what it was. But, we've also had some rain which washed away pollen from around the pool deck/slide/diving board/etc. So, I couldn't say for certain that it was pollen. It definitely had the color of pollen. And, I don't know if this matters, but while there was a fine layer of pollen/algae across the entire bottom of the pool (Only visible when underwater with a mask on), it had congregated in all the divots in the pool floor. That led me to think it was floating down from the top.

When you say evaporation, are you actually losing water in the pool? Do you see it go down?

Yes. I haven't measured, but I'd say I lost 2" in the past 5-7 days. I verified it's not a leak with the bucket test. Steam is rising off the pool quite a bit these days (Shutting off heat soon).

And capricatunes, what did you mean by "that’s never happened before?" How many times have you had to SLAM? And how many days, months, years apart?

How often are you testing? And how many times a day is the FC dropping well below SLAM level.

  1. I've SLAMmed twice before over 1.5 summers. Once after a flash flood, and once when I bought the home last summer. Both times took two days to pass the OCLT. Both of those were due to cloudy water and there was high pollen count (but no visible anything on the bottom).
  2. During SLAM, I've been testing 3 - 4 per day. But, I can't seem to keep it above 16.5. I even added 128oz of 12.5% when I was at 15.5 FC, tested ~3hours later (Without direct sun) and my FC was 16.5.

If all the visible signs of algae are gone, then you go hunting for it. Behind light fixtures, inside ladders, under drain covers, inside the skimmer, behind the weir door, etc.

I went hunting and found nothing so far. I've hunted twice, but it's possible that I'm missing it.

Did we ever answer capricatunes question? I've never read here that the SLAM process, or the end-of-slam criteria were affected by cold air temp.

Thanks, I would still love to know if evaporation and coldness affect FC and SLAM.

A new idea: does chlorine automatically lower/balance itself based on your CYA? When I last measured my CYA (pre-SLAMM), I was on the fence between a CYA of 30 or 40. So, now I'm thinking, "Huh, perhaps my CYA was 30 not 40, and maybe my SLAM should be 12 not 16...so is it possible the FC is automatically finding equilibrium at 12 due to a lower CYA?" I am sure this has been discussed elsewhere, but I'm unable to find what I'm looking for.

Thanks a lot for all your help.
 

mknauss

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May 3, 2014
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does chlorine automatically lower/balance itself based on your CYA?
No. The FC can be lost to UV during the day at a higher rate if CYA is very low. But at night, FC will stay in the pool with 0 CYA if no organics.
 

capricatunes

Bronze Supporter
Jun 3, 2020
28
Minneapolis
No. The FC can be lost to UV during the day at a higher rate if CYA is very low. But at night, FC will stay in the pool with 0 CYA if no organics.

Blurg. I must have something eating that chlorine somewhere. Perhaps I need to remove my light like this person? Think I may have found my FC demand issue? Otherwise, any advice for how to check if there's something in my filter, pipes, or pump?

And here's something curious, my FC actually stayed _more_ steady all day yesterday - even during a sunny day. I lost about 2ppm during the day, but then between 10pm - 8am I lost 3.5ppm.
 

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mknauss

Mod Squad
TFP Expert
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Laughlin, NV
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If you have a light in a niche, that is the prime spot for algae to hide and to confuse a pool owner. Take the light assembly out and clean the niche.
 
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capricatunes

Bronze Supporter
Jun 3, 2020
28
Minneapolis
Well I finally found something - not sure if it's the only culprit.

We had a crack form on our stairs this year. As a temporary fix, I used vinyl patches and glue. It's held for the summer, and my plan was to repair the crack permanently in the spring - it's the second from top step so the water will be well below for the winter. I had an object setting on top of that patch to alert the kids not to step on that area. I had previously looked under that object as a prime suspect but found no algae. But, I missed it. There is algae on the patch. Also, it would seem some of the algae is between layers of the vinyl patches. It's not much (Hence not seeing it before), but it is green.

I just scrubbed the heck out of that area and added bleach to that area directly. However, I can't scrub it all away because some of the discoloration is between/under patch layers. Some was on top and I scrubbed that off. So....
  1. Do you think it's possible to kill that algae without tearing that patch off? I also set a puck directly on the patch to see if that might help ensure chlorine is hitting that spot. Any other tips here?
  2. Does this mean there is living algae in the entire pool water?
    1. I'm asking because I wonder if I can winterize my pool (That would get the water below the stair patch) - or if that would cause big problems, because the filter would obviously not be running any longer, so perhaps I'm closing a pool full of (albeit invisible) algae? We were planning on winterizing soon, so I'm not sure what my move here is based on question #1...
Thanks for all your encouragement and help!
 
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