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Thread: Calc setting on SWG when CL output at 100% is 24 gm/hr

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    Calc setting on SWG when CL output at 100% is 24 gm/hr

    I have a curly one that is a little beyond me but might be pretty straightforward to you guys and would appreciate the help.

    I have a Zodiac LM3-24 salt water generator which is rated at 24 grams of Chlorine per hour at full output. It has 5 levels of output and I assume that level 5 is 24 gm/hr, level 4 is 19.2 gm/hr ..... level 1 is 4.8 gm/hr. To regulate the output of chlorine, I can vary both hours per day and the output level. It is oversized for my pool at 12,700 gallons/48,000 litres but that is what I have and was a few hundred dollars cheaper than the smaller one recommended for my pool.

    How do I work out how many hours to run it at and at what setting to raise the FC level a certain amount?

    On the pool calculator, down the bottom, if I select 73% cal-hypo and 33 grams (is that the same as ~24 grams of 100%??) it says that FC is changed by 0.5. Do I then assume that I am increasing FC by 0.1/level/hour on my SWG. So if I run it for 4 hours at level 1, I am changing FC by 0.4 (same as adding 26.3 grams of 73% cal-hypo??). At the top end, if I run it for 8 hour at level 5, it would increase FC by 4.0. The superchlorinate button runs it for 24 hours at level 5 so I think I want to stay away from that (raise FC by 12.0). In any case, do those numbers work or is it not as simple as that?

    I test the water once a week on the weekend and would then set the SWG to run for the week based on that setting.

    Currently CYA - 39, FC - 4.4, pH- 7.5, TA - 130, CH - 330 (was 260 last week so am a bit suspicious of the pool shop testing on that one)
    48,000 litre (12680 gal); Hayward 24" Sand Filter; Zodiac/Clearwater LM3-24 SWG
    Inground Q-Quartz/Quartzon Plaster; 0.75HP Pump; 62 GPM filter

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Calc setting on SWG when CL output at 100% is 24 gm/hr

    The grams of chlorine they refer to when talking about SWG output is grams of chlorine gas. 24 grams/hour in 48,000 liters is 0.50 ppm FC which I believe is what you were looking for. As for varying hours per day vs. output level, it doesn't matter which way you go in terms of total output so long as the product of % on-time times hours per day running is the same. From a circulation point of view it would be better to have the hours per day longer (i.e. more turnovers) if your pump is variable or 2-speed so it doesn't cost you so much. Basically, I'd set your hours per day at what you need/want for circulation (turnovers) and then adjust the output level accordingly. All the output level does is cycle the SWG on/off during the hours per day the pump is running. When the SWG is on, it's fully on -- there is no being partially on or having partial output.

    Though I gave you a guide to figure out FC per hour, that is only a rough guide if you know the FC per day usage. If it's 2 ppm FC per day, for example, then you'd need the SWG to be on for 4 hours at 100% output level or 8 hours at 50%, etc. If it's 1 ppm FC per day, then the hours or output level would be cut in half.

    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Calc setting on SWG when CL output at 100% is 24 gm/hr

    Keep in mind that actual chlorine production will vary somewhat depending a whole variety of factors, so calculations like this one are never as exact as they appear to be. You can use such a calculation as a starting point, but in the end what matters is the actual FC level of the pool, not what the calculations said it ought to be.
    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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