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Thread: Pool is clear but overnight test still fails

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    Pool is clear but overnight test still fails

    I've noticed some algae on the bottom of my pool few days ago. It wasn't much and the water was still clear all the way to the bottom. As advised here I started a SLAM process. I actually miscalculated a bit and instead of advised 20ppm SLMA level took it all the way to 30ppm.

    After two days of SLAMing the water is absolutely clear there is nothing on any walls or bottom, but my overnight test still fails. Last night between 8pm and 7am it dropped by 5.5 ppm.

    Any advice on what else I could do or what could be causing this?
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Agent99's Avatar
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    Re: Pool is clear but overnight test still fails

    Check all nooks and crannies. Check under ladders, inside light niches, and inside the skimmer and see if you find any algae lurking there continuing to use up chlorine. Then brush 'em out and get them floating so they can be killed.

    What is your CC reading?
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    Re: Pool is clear but overnight test still fails

    Thanks. I took out the light and cleaned inside (it was actually clean) cleaned steps, cleaned everything like you said. Haven't checked inside autofill yet. that's a good idea actually.

    my CC reading is 0.5 and it's been at 1 before I started SLAM
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Re: Pool is clear but overnight test still fails

    Just keep the SLAM up, it takes a few days sometimes to pass that OCLT.
    My Amazon Smile for November12K Fiberglass IG, Infinity 4000 automatic cover, SWCG, Hayward Sand Filter, Hayward 1.5 Pump, Doheny Discovery Robot, Savi Melody LED pool lights, outdoor speakers and other assorted doo-dads. Sundance Altamar Hot Tub.
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    Re: Pool is clear but overnight test still fails

    Great. So you've passed 2 of 3 criteria for the SLAM. Keep it going until the OCLT is 1 ppm or less. Hopefully you find something hiding but even if you don't, keep SLAMing.
    ----Chris----
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    Re: Pool is clear but overnight test still fails

    Just went and checked the autofill. it looked pretty clear, but I brushed it and put some clorox right in there.
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Mod Squad tim5055's Avatar
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    Re: Pool is clear but overnight test still fails

    Chlorine demand and OCLT tell us when things are wrong with the water. I had to SLAM this year because,of a stupid mistake but the water was always sparkles clear. I just noticed a higher chlorine demand, proved a problem with the OCLT and started the SLAM. Even with beautiful water it took me 4 days to eradicate whatever was in there.

    Trust your testing. If you fail OCLT there is a reason.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Pool is clear but overnight test still fails

    Thanks, Tim, that's encouraging.

    One thing that came to mind. Could agae be lurking in my filter? Should I clean the filter. Mine is DE and backwashing it a bit tricky as you never know how much DE to add. Pressure on filter shows that it's fairly clean.
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Re: Pool is clear but overnight test still fails

    Quote Originally Posted by zhenya View Post
    Thanks, Tim, that's encouraging.

    One thing that came to mind. Could agae be lurking in my filter? Should I clean the filter. Mine is DE and backwashing it a bit tricky as you never know how much DE to add. Pressure on filter shows that it's fairly clean.
    I don't think algae can live in the filter due to zero sunlight. Besides, you're passing SLAM water through it 24/7. It probably has better exposure than some parts of the pool.

    Hang in there .........

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    Re: Pool is clear but overnight test still fails

    Quote Originally Posted by tim5055 View Post
    Chlorine demand and OCLT tell us when things are wrong with the water. I had to SLAM this year because,of a stupid mistake but the water was always sparkles clear. I just noticed a higher chlorine demand, proved a problem with the OCLT and started the SLAM. Even with beautiful water it took me 4 days to eradicate whatever was in there.

    Trust your testing. If you fail OCLT there is a reason.
    +2 I had a couple of times this summer with the same thing. Higher chlorine usage and had to do a couple of SLAMS. I never noticed a difference in my water but something was brewing.
    16x32 IG rectangular 21,800k new vinyl liner 2014, Triton II TR 50 sand Filter, Pentair 3/4 hsp whisperflow pump, 3 returns, TF100 test kit w/speedstir. Maytronics s 300i robot.

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    Mod Squad tim5055's Avatar
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    Re: Pool is clear but overnight test still fails

    Quote Originally Posted by Chrissykr View Post
    +2 I had a couple of times this summer with the same thing. Higher chlorine usage and had to do a couple of SLAMS. I never noticed a difference in my water but something was brewing.
    Yea, I know,what caused mine. 4 day weekend out of town and I had turned off the Stenner pump to do some work before I left town....

    4 days in the hot SC sun with no chlorine.......
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Pool is clear but overnight test still fails

    Quote Originally Posted by domct203 View Post
    I don't think algae can live in the filter due to zero sunlight. Besides, you're passing SLAM water through it 24/7. It probably has better exposure than some parts of the pool.
    It's true that the algae won't grow in a filter, but that doesn't mean that chlorine isn't still oxidizing the dead algae. If a filter is full of debris that chlorine can react with, it is best to backwash or clean (as appropriate) the filter.
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    Re: Pool is clear but overnight test still fails

    Also remember that there could be other things in the filter that will consume chlorine. I kept having a mystery chlorine demand this summer, ended up opening up my DE filter to find the DE was saturated with some sort of oily substance, I don't know what it was or where it came from, but there was a LOT of it.
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    Re: Pool is clear but overnight test still fails

    Quote Originally Posted by zhenya View Post
    After two days of SLAMing the water is absolutely clear there is nothing on any walls or bottom, but my overnight test still fails. Last night between 8pm and 7am it dropped by 5.5 ppm.
    Q: What test kit are you using and what sample size did you use to do the overnight? Do you have one of the recommended test kits?
    Q: What concentration are you using and have you checked the time stamp on the bottles? Sometimes, the calculations could be off because the % strength is not accurate.
    Q: Have you verified the size of your swimming pool?

    Any variables in these items could cause an error. Also saw that you had an 11 hour time lapse between testing? Maybe shorten the time to 1/3 (8 hours). If all these are fine, then something is definitely lurking in that water.
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    Re: Pool is clear but overnight test still fails

    I am using Taylor Kit. Using 10ml sample size
    My chlorine is 8.25% purchased at Costco
    I verified the size of my pool several times, but how would it be relevant. I am comparing results between two different tests using the same pool, same chemical, etc.

    It's now been 5 days and still the same trouble with overnight test. I am loosing patience not to mention kids are ready to kill me because I don't let them swim. I am going to do a full filter clean on Wed so hopefully it solves the problem. I don't know what else can possibly cause chlorine disappearing so quickly. The pool is perfectly clean all around.

    Thank you all for your suggestions. Would love to hear more ideas of what I might be doing wrong.
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Re: Pool is clear but overnight test still fails

    Well zhenya, here's a thought for you to consider because it happened to me personally. Since I didn't notice your current CYA anywhere on this thread, it may be relevant to you as well. Earlier this season I kept failing my OCLT. So much so that I went through almost TWO bottles of R-0871. I was going nuts! Why? Because as you noted in post #1, I too was over-shooting my SLAM FC by waaaaaay too much. So much in-fact that even though I had no apparent loss to algae, some of my excessive FC had to drop in relation to the CYA. If my SLAM FC was 24, I had my FC at night as high as 35 or more. When it comes to the OCLT, more is not always better.

    So unless I missed it somewhere, we don't know what your actual CYA is right now. But whatever it is, definitely make sure you are not exceeding the corresponding SLAM/Shock FC level for that CYA as listed on the Pool School - Chlorine / CYA Chart. If you go too high on your FC, then you might lose more than 1ppm of FC. Example: If your CYA is 50, then don't go over an FC of 20. Anyways, once I realized I was simply going way too high, the very next night I let my FC come down to the regular SLAM level, and passed the very next morning. Maybe that will help you. Good luck.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    Re: Pool is clear but overnight test still fails

    Texas, splash, that might be it. I have been overshooting my FC. My CYA is 30 which give me a target of 16. I've been keeping it at around 25 thinking i'll kill whatever it is faster.
    27K gal, IG pebble, Jandy JEP2.0 VS ePump, Jandy DEV60 filter, Jandy SW with ChemLink C1900, Zodiak MX8 vacuum
    The pool was repiped and new equipment installed Nov 2013.

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    Re: Pool is clear but overnight test still fails

    Exactly. Me too. Drove me nuts. Not sure if the FC will lower fast enough for you before the sun goes down on the west coast, but if not, definitely let it come back down and try it tomorrow at the proper level. Say, you might want to double-check the CYA chart unless that was a typo above. A CYA of 30 calls for a SLAM/Shock of only 12. An FC of 16 is for the CYA of 40. Either way you've been a bit high, so maybe that will help you pass next time. Good luck!
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    Re: Pool is clear but overnight test still fails

    And of course ... if you still happen to fail the OCLT later, try not to be too discouraged. Not all bad stuff in the water is visible to the naked eye. It just means your bleach is still cleaning the water for you and the kids. You'll get it. But I hope the correct FC level does the trick for you.
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    Re: Pool is clear but overnight test still fails

    As for frustrated swimmers, keep in mind that it is safe to swim with FC up to shock level, as long as the water is clear enough for decent visibility. Of course, it sounds as though you have been running well above shock level for your CYA much of the time... Maybe this is another incentive to stay closer to the recommended level. Let it drift just below shock level, let kids swim, boost it back up a bit after they're out.
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