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Thread: Trouble with SWG Math

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    Trouble with SWG Math

    Having a hard time figuring this out........

    My SWG claims a production rate of 1.38 lbs. per day. ( I assume this means when the dial is set to 100%)

    I've had good success running my pump 10 hours per day with the SWG set at 50%. So I did some math.......

    1.38 lbs./day = 22 oz./day of chlorine gas (this is the term used in the PoolMath calculator)

    So, according to PoolMath, 22 oz. Chlorine gas/day should raise FC by 7ppm each day if I run the unit at 100%

    Now, back to what I actually do....run 10 hours at 50% output.

    10 hours @ 100% should produce about 9.2 oz of chlorine gas
    Therefor 10 hours @ 50% should produce 4.6 oz of chlorine gas

    According to PoolMath, 4.6 oz of chlorine gas should raise the FC by a little less than 1.5ppm.

    However, I'm pretty sure I have more than 1.5 FC loss each day as I measured it (without the SWG turned on) to be closer to 2.5 - 3.0 FC loss per day. But the 50% setting seems to be maintaining my FC at around 7.0ppm over the last several days.

    Can anyone point out where my math or any assumptions I use are incorrect?
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Richard320's Avatar
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    Re: Trouble with SWG Math

    Nothing wrong with the calculations.

    So either the pool is much smaller than you think, your SWG is bigger than it says it is, or poolmath has an error somewhere.

    When you add other chemicals, does poolmath figure things correctly? If you want to be dead certain of the volume: A Chemical Way of Calculating Pool Volume
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Swampwoman's Avatar
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    Re: Trouble with SWG Math

    Hi Run!
    Re:
    However, I'm pretty sure I have more than 1.5 FC loss each day as I measured it (without the SWG turned on) to be closer to 2.5 - 3.0 FC loss per day. But the 50% setting seems to be maintaining my FC at around 7.0ppm over the last several days.
    You're using the same math I've been using to dial in/ down my new swg and you're experiencing similar results.

    I seem to only be "using" about 1.5 ppm per day whereas before swg I was def more like an average of 2.5 with many days closer to 3.

    I was debating earlier today to myself that this either meant my math was bad, OR maybe the beauty of constant chlorination is that with the higher cya and lower "dose" levels, much less chlorine is "wasted" via UV exhaustion.

    I'm hopeful the latter is true...and it makes sense to me.
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    JoyfulNoise's Avatar
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    Re: Trouble with SWG Math

    Daily FC loss rate can look a lot like the stock market Dow Jones data - one day it's up, one day it's down then back up again, etc, etc. it's the trends and averages that are important. Bather load, temperature and sunlight all have a part to play. In a clean, unused pool with high CYA and the standard TFP recommended levels for an SWG, FC loss can be as low as 1ppm/day. Throw in some wind-blown foreign matter and a few kids and that loss will increase.

    Also, as Swampwomam points out, the consistent dosing of FC and oxidation caused by an SWG cell tends to show lower daily FC loss than the fluctuating chlorine levels found in a manually dosed pool.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Mod Squad pooldv's Avatar
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    Re: Trouble with SWG Math

    It is true that the higher the chlorine level the faster the rate of decay. One of the reasons why we don't recommend going over shock level during a SLAM. Was your CYA at the same level for the 2.5 ppm use vs the 1.5 ppm rate?
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    Re: Trouble with SWG Math

    Quote Originally Posted by pooldv View Post
    It is true that the higher the chlorine level the faster the rate of decay. One of the reasons why we don't recommend going over shock level during a SLAM. Was your CYA at the same level for the 2.5 ppm use vs the 1.5 ppm rate?
    Yes.....CYA has been 45 throughout. When I opened, I slammed so kept the CYA where it was from over the winter. Now that I've passed all 3 SLAM tests (my annual opening ritual) I will start to bump CYA to about 70-80.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Mod Squad pooldv's Avatar
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    Re: Trouble with SWG Math

    Raising CYA will further reduce your daily chlorine loss. It just keeps getting better!
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    Re: Trouble with SWG Math

    Quote Originally Posted by pooldv View Post
    Raising CYA will further reduce your daily chlorine loss. It just keeps getting better!
    Yes

    Will be doing that this weekend
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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