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Thread: Turn off SWG after Shocking and Passing OCLT?

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    Turn off SWG after Shocking and Passing OCLT?

    First year pool owner. I've read through Pool School countless times and done a variety of searches, but haven't seen an answer to this specific situation.

    I recently went through my first battle with algae. We had a big storm blow through on Tuesday and found my skimmers filled with leaves on Wednesday afternoon. Pool was cloudy, but I decided to let it ride out the night with the pump running non-stop only to find it worse when I got home yesterday. I shocked with bleach last night, boosted it back up this morning and my water is now back to crystal clear. I think I was very fortunate to catch this so early. I still have to get through an OCLT tonight, but assuming I pass, I've seen varying advice on when to turn by SWG back on? Some say to turn it back on once I pass the OCLT since my FC level will drift back down naturally over a few days. Others recommend leaving it off until back in my target range. Logically, I think the latter makes more sense (leave the SWG off until back in target range), but my analytical side wants to know for sure. If I pass the OCLT and turn my SWG back on tomorrow morning, wouldn't I effectively be holding my FC level constant from that point on? Isn't that the goal of the SWG, to replenish FC levels to the target range each day? Conversely, if the consensus is that my FC level will continue to drift down even with the SWG on, then what prevents me from ultimately going below the target range?

    Thanks in advance for satisfying my curiosity.
    20x40 Roman Shape Vinyl IG Pool, 30,000 gallons, Pentair Intelliflo VS+SVRS, Triton II TR60 Sand Filter, Pool Pilot Digital SWG with RC-42 Cell, Blue Diamond Robot

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    Mod Squad jblizzle's Avatar
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    Re: Turn off SWG after Shocking and Passing OCLT?

    Welcome to TFP!!!

    The CYA level kind of sets the % of the FC that is lost to the sun each day. When you are at a higher FC level, you will lose more ppm of FC than you will have lower FC levels. The SWG is adding certain # of ppm each day. If you turn it on while at a higher FC level, you will be adding #ppm FC, but will be losing more ppm to the sun than you will at lower FC levels. So, the FC should still drop with the SWG on although slower than if you were not adding FC.

    Really does not matter either way. You just have to make sure the SWG is set correctly to maintain the correct normal FC levels.
    Jason, TFP Moderator
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    JasonLion's Avatar
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    Re: Turn off SWG after Shocking and Passing OCLT?

    It makes very little difference if you turn on the SWG after passing the OCLT, or when your FC level gets back to normal. Right away is better because that way you won't forget. Waiting until FC comes down to normal is better because that will use less total chlorine, and thus extend the cell life just a tiny bit. Either way not a big deal.

    The final FC level depends on your percentage setting, not on the starting FC level. The higher your current FC level the faster you lose chlorine. The FC level will always drift down to the level where FC losses exactly match the amount of chlorine the SWG is adding.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Turn off SWG after Shocking and Passing OCLT?

    Ahhh. Thanks to both of you. Seems so simple now to read it.

    Just for laughs, I had to drop my son off at camp today and was going to be near the pool store. I took in a water sample and explained that my water was cloudy, but it seemed to be improving after shocking last night. They tested the water and told me the reason it was cloudy was due to high phosphates. I asked if it was the phosphates making it cloudy or the stuff feeding on the phosphates. They claimed the phosphates themselves were the cause and wanted to sell me phosphate remover. Fortunately, I was armed with the knowledge from this site and resisted the hard sell. I told them I'd give it another day and if things got worse, maybe I'd be back in. They countered that I'd spend far more on choline (bleach) than I would on their phosphate remover, but I still walked out empty-handed. Just one more example of why we're wasting our time and money getting advice from the pool stores.
    20x40 Roman Shape Vinyl IG Pool, 30,000 gallons, Pentair Intelliflo VS+SVRS, Triton II TR60 Sand Filter, Pool Pilot Digital SWG with RC-42 Cell, Blue Diamond Robot

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    JasonLion's Avatar
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    Re: Turn off SWG after Shocking and Passing OCLT?

    Entertainingly, the only real world situation where phosphates will cloud up pool water is when you add phosphate remover. Leave the phosphates alone, and they will leave you alone
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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