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Thread: PoolMath issue--how many gallons?

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    tdp's Avatar
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    Unhappy PoolMath issue--how many gallons?

    Because of trees, we don't get direct sunlight on our pool until about 8:45 AM. Does the ambient light between sunrise and 8:45 have an effect on FC in an OCLT?
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    tdp's Avatar
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    Unhappy PoolMath issue--how many gallons?

    I had to start a SLAM last night (very discouraged about that, but that's for another thread). The manufacturer's specs for my fiberglass pool say that my pool capacity is 18K gallons, but the installer said that means when the pool is filled to the very brim, which (hopefully) never happens in real life. My pool is an irregular shape, so can't just do length x width.

    I made a guesstimate and have been using 16K gal. in PoolMath. For my CYA (average of 3 tests was 65), PM said to add 420 oz. of 10% to get SLAM FC level, which is 26. I added 3-128 oz jugs and then measured the rest with a glass measuring cup.

    Two hours later (~10 PM), I tested the FC and it was 32.5, not 26 (pump had been on whole time). I played around with PoolMath, and to get that level of FC, it says 12225 gallons! That would mean my pool was only about 2/3 full, which it clearly isn't.

    I am confused.
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: OCLT and ambient light

    Quote Originally Posted by tdp View Post
    Because of trees, we don't get direct sunlight on our pool until about 8:45 AM. Does the ambient light between sunrise and 8:45 have an effect on FC in an OCLT?
    Regarding ambient light, I would say that FC is slightly affected, but not enough to make a difference with regards to how much FC you consume.

    Are you failing the OCLT? If so, at what level are you testing?

    I know that at higher levels (FC of 15 or higher, it is sometimes more difficult to pass the test). I can not pinpoint the thread, but if this is the case, I would recommend allowing the FC to drop down to a lower level. In addition, taking your time with your testing is essential, because testing error does occur.
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
    Hayward Pro-Series 350 LB. Sand Filter Model # S270T - 2" Plumping
    Hayward CL2002 Chlorinator - Hayward Super Pump 2 HP Model # k48m2n111
    Hayward AQR9 SWG 25K Salt Cell & TF-100 Test Kit + Speed Stir
    Gulfstream HE125RA - 117K BTU Heat Pump - Date of Build is 11-2013

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    Texas Splash's Avatar
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    Re: PoolMath issue--how many gallons?

    When you were using the calculator, did you ensure to manually update the "WEIGHT" field for the correct bleach percentage you added?
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Re: PoolMath issue--how many gallons?

    Are you talking about "or add x by weight or unknown by volume of x"?

    Not sure why that is applicable, since I'm not adding any form of dry chlorine?
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    On the FC row, you have to manually enter "8.25", "10, or 12, whatever percentage liquid bleach you are using. By default I think it goes to "6".
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Re: PoolMath issue--how many gallons?

    Yes, I am using 10%, and have set PoolMath to 10% trade (not sure what "trade" means, but I can't edit that field).
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    Okay, so when I check PM it tells me that in an 18K pool ( I know you tried 16K), 3 gallons of 10% will increase FC by about 16-17 ppm. PM is quite accurate with those numbers. My pool is 17,888, so I just used that factory figure even though I only go halfway up the skimmer. 2-3 inches down might be a few hundred gallons, but not earth-shattering overall.

    What was your starting FC before you added the 3 gallons last night?
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Re: PoolMath issue--how many gallons?

    5.5 FC before additiob


    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    Oh, and I just realized ... was your SWG "OFF" during this period last night? Did you add bleach AND have the SWG on? That could explain the higher FC right?
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Re: OCLT and ambient light

    I started SLAM last night and failed OCLT big-time this AM (FC dropped from 32.5 at 10 PM to 28 at 6:30 AM). My SLAM level was actually supposed to be 26, but something is up with my PoolMath--for some reason, I can't copy/paste the link to my other thread about the PM problem on iPad, but it's in Testing and balancing your water>Pool Math issue--how many gallons?
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    No, I turned SWG off before adding the chlorine last night, and pump is running 24 hrs. now for SLAM


    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    Also, I waited 2 hrs. between adding the 420 oz of Cl and testing FC level


    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    How much FC was in the pool before you did the dose?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    tdp's Avatar
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    Re: PoolMath issue--how many gallons?

    5.5 FC as in PP
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    Okay, so I duplicated everything you did and it matched. Honestly, I'm not sure how to explain that over-shot. Since you were using a smaller size volume to be safe, you would think that your FC test after adding bleach might actually be "under" your goal as opposed to over. I agree that there's no way your pool is closer to 13K. I wonder if perhaps the bleach you got just happened to be a bit stronger? Normally it gets weaker, but you never know. There has to be an explanation, but I'm just not seeing it. Maybe I need more caffeine.

    A couple other things I think you might want to consider next time though:
    - Increase your pool volume to about 17500. 18K factory spec, reduce enough to compensate for mid-way up the skimmer (3-4" maybe), but I don't think that's 2K-worth of water is it? Your call though.
    - Round-up your CYA to 70 and use an FC of 28 as your SLAM. We never split the vial measurements, it just gets messy.

    If I see anything else that may apply I'll let you know. Good luck on your SLAM.
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Re: OCLT and ambient light

    If you started the SLAM last night, probability says you will not pass the OCLT. How is your water? Why did you perform the SLAM to begin with? Is your water green? When performing the test, take your time in adding the reagents. At higher levels, you could be faced with more testing error. Please take a step back and describe the events that led up to the SLAM. Thanks!
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
    Hayward Pro-Series 350 LB. Sand Filter Model # S270T - 2" Plumping
    Hayward CL2002 Chlorinator - Hayward Super Pump 2 HP Model # k48m2n111
    Hayward AQR9 SWG 25K Salt Cell & TF-100 Test Kit + Speed Stir
    Gulfstream HE125RA - 117K BTU Heat Pump - Date of Build is 11-2013

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    Re: PoolMath issue--how many gallons?

    5.5 FC as in PP
    Sorry, I completely overlooked that post.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    tdp's Avatar
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    Re: PoolMath issue--how many gallons?

    Thanks, I appreciate all of your replies.

    I just rechecked the specs of my pool online, and 18K is indeed the right figure. When I first started with TFP last fall, I was actually using 14K, since when the installers originally filled the pool, they said it took two trucks of 7K gallons each. I revised that upward to 16K after a while because I had a feeling that 14K was too low so I split the difference.

    Now I am a little nervous about using PoolMath
    ~17,500 gal. IG Fiberglass, Viking "Cambridge"; installed 6/2015
    SWG Hayward Turbo Cell T-9
    Hayward Hi-Rate Sand Filter
    Hayward Max-Flo XL pump
    TF-100 Test Kit/SpeedStir

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    Re: PoolMath issue--how many gallons?

    Assuming you're using the Poolmath from the home page tab and not some outdated version on-line, it's a great tool. It took me some practice to fine-tune my PM skills and ensure I had my pool volume close, but now I've got it dialed-in to where when I add X-amount of bleach, it just about hits it every time. Same for acid (pH) adjustments or anything else. In fact, I would encourage you to watch all those numbers (before & after) as you try other adjustments. Maybe you'll see something that will help explain why the bleach thing was giving us odd numbers. The only other factor I never mentioned in all of this was testing error, but I'm assuming your FC testing is rock-solid by now. You'll get it I'm sure. Have a nice day.
    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
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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