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Thread: 2ppm drop overnight

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    2ppm drop overnight

    Hi there,

    My water is still clear, but I noticed my FC dropped more than usual the other day, so after adding bleach and waiting an hour I tested last night at 10ppm, no free, PH of 7.8.

    This morning I tested early to get an idea if an overnight loss and it came up at 8ppm. 2 overnight, but the water looks great!

    Is this because my PH is high, reducing the chlorine effectiveness? Should I SLAM the pool? Or is there a different, less involved way to keep things in check when the water is clear?
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    JasonLion's Avatar
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    Re: 2ppm drop overnight

    A 2 ppm loss overnight measured with a FAS-DPD chlorine test means that something that shouldn't be there is consuming chlorine. It wouldn't have anything to do with PH. None of the other chlorine tests have enough precision to do an overnight loss test.

    Could you post a complete set of water test results?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: 2ppm drop overnight

    I will collect a fresh test set tonight after sundown. I was using FAS-DPD last night and today for my chlorine check. It was daylight by the time I tested today but mo direct light on the pool yet (about 8am from 1230 the night before).
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Re: 2ppm drop overnight

    Okay Jason (and everyone else), I ran a set of tests tonight, water sampled after the pump had been on 3 hours. Oh and FWIW the skimmer basket was jammed full of leaves - part of the problem?

    FC 5.0 (EDIT2: was 8.0 this morning, 10ppm last night)
    CC 0
    pH 7.4 (I added muriatic acid at 8pm b/c I knew it was high from last night)
    TA 150
    CH 175
    CYA 100 (Edit: This can't be lowered, my wife refuses to let me "waste" water. She hates the pool and doesn't care what the cost of the chlorine and effort is on my part since she never uses it)

    So 2ppm overnight, and another 1ppm in the day. I re-read the SLAM and since my OCLT is > 1.0, I figure I need to keep at it. My question for the forum is if I should go to 39ppm per the chart or if a "mini" slam is all that's needed when water is clear?
    Last edited by Gig103; 06-25-2014 at 01:22 AM. Reason: 1)CYA detail, 2) FC detail
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Mod Squad jblizzle's Avatar
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    Re: 2ppm drop overnight

    How confident are you that the CYA is only 100 and not higher?

    You need too SLAM to the full shock level. Although very odd (impossible?) that you lost less during the day than overnight.
    Jason, TFP Moderator
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    Re: 2ppm drop overnight

    Quote Originally Posted by jblizzle View Post
    How confident are you that the CYA is only 100 and not higher?

    You need too SLAM to the full shock level. Although very odd (impossible?) that you lost less during the day than overnight.
    Thanks for confirming that the full level is required even when the water is clear.

    Meanwhile I am confident in the 100. I used a half sample and it came up as 50. I haven't put anything but bleach in since Memorial Day when I started reading Pool School. I will make sure the chlorine is 39ppm tonight and check it in the morning. I know that isn't ideal monitoring frequency when starting a SLAM, but I will see what happens.

    - - - Updated - - -

    Quote Originally Posted by jblizzle View Post
    How confident are you that the CYA is only 100 and not higher?

    You need too SLAM to the full shock level. Although very odd (impossible?) that you lost less during the day than overnight.
    Jason I checked my notes and you are right. It was 10ppm last night, 8ppm this morning (when I posted the thread), and 5ppm tonight.
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Re: 2ppm drop overnight

    So, a question about the Taylor test kit... Today around 60 drops the water went to a tan color. Did I do something wrong or is it just incapable of turning truly clear at such high concentrations of FC?
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    JasonLion's Avatar
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    Re: 2ppm drop overnight

    Tan/brown means you didn't use enough of the R-0870 powder.
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    Re: 2ppm drop overnight

    Hrm, It turned a nice vibrant color when I used my rounded scoop. I will be more generous tonight.
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Re: 2ppm drop overnight

    Could you possibly water the yard, garden, flowerbeds, foundation, etc. with the pool water? Over time you'd get the CYA down to where you need it.
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    Re: 2ppm drop overnight

    A more generous scoop of R0870 had a proper test result. Something is still chewing up chlorine and I'm not sure what. My wife commented how nice the pool looked today - could it be the cartridges in need of a rinse? If so, is it okay to stop the pump for 30 or so minutes to spray them off? Rules do say to run non-stop!
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Mod Squad jblizzle's Avatar
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    Re: 2ppm drop overnight

    You have to clean the filter when the pressure rises 20-25% over the clean pressure.
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    Re: 2ppm drop overnight

    Gotcha... Ignoring the actual rule of thumb though (for my own information) can the debris in a cartridge be enough to eat algae? And if so, what if it's not "due" for a cleaning?
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Re: 2ppm drop overnight

    Filters do not eat algae.
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    Re: 2ppm drop overnight

    I'll second the water the lawn etc. comment. Not wasting if you're watering!
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    Re: 2ppm drop overnight

    Quote Originally Posted by jblizzle View Post
    Filters do not eat algae.
    Well shoot if I didn't ask that wrong... If there is algae or other debris in a cartridge could that explain the chlorine eating?
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Mod Squad jblizzle's Avatar
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    Re: 2ppm drop overnight

    It will consume some chlorine if there are organics trapped in the filter. As I said, you need to clean it when the pressure rises which indicates that stuff is trapped in it.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: 2ppm drop overnight

    I like sharing happy ending... I had a successful SLAM as it passed an OCLT and the cartridges are cleaned.
    ~12,000 gallon IG pebble pool. Pentair CnC Plus 4-cartridge system, AO Smith 1.5hp single speed

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    Mod Squad jblizzle's Avatar
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    Re: 2ppm drop overnight

    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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