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Thread: SWG and automatic pool cover

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    AZ Pool Boy's Avatar
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    SWG and automatic pool cover

    Anybody out there running a SWG on a pool with an automatic pool cover? Man, I'm getting some wild chlorine level swings depending on how much the pool is open.

    Since it's gotten cooler, we're only using our pool once a week or so. I'd been running my SWG at 15% previously. But now that we're not opening the pool cover is much, my chlorine has been off the charts. Last night it tested at 8ppm. I finally shut the SWG off completely, opened the pool and ran the water features for a while to try to aerate the pool and lose some chlorine. Today it's still way high. I'll be testing the level daily until it comes back down. But I'm guessing I'll have to lower the level well into the single-digit percentages to keep my chlorine reasonable as the weather gets cold and we're not using the pool much.

    Anybody else dealing with this situation?

    Thanks,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    donaldm823's Avatar
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    Re: SWG and automatic pool cover

    Quote Originally Posted by AZ Pool Boy
    Anybody out there running a SWG on a pool with an automatic pool cover? Man, I'm getting some wild chlorine level swings depending on how much the pool is open.

    Since it's gotten cooler, we're only using our pool once a week or so. I'd been running my SWG at 15% previously. But now that we're not opening the pool cover is much, my chlorine has been off the charts. Last night it tested at 8ppm. I finally shut the SWG off completely, opened the pool and ran the water features for a while to try to aerate the pool and lose some chlorine. Today it's still way high. I'll be testing the level daily until it comes back down. But I'm guessing I'll have to lower the level well into the single-digit percentages to keep my chlorine reasonable as the weather gets cold and we're not using the pool much.

    Anybody else dealing with this situation?

    Thanks,
    AZ
    I saw similar results when I started using my solar cover at night. Had to lower my SWG to 30% (I have a SC-60 with a 30,000gal pool). Also somedays it goes higher than the trend, and sometimes lower. I have been attributing that to mixing since the solar cover does effect the pool water flows/mixing when I get a sample. My biggest benefit of the cover is that my pH stops going up! I also have seen CC start to climb-now at 0.2ppm after 1 week of solar cover, where as is was always 0ppm-think that is due to the low amount of run time of the cell since my Autopilot is auto temp compensated-sometines the run time dips into the 15% range if the pool water is cold in the morning.
    Don SW Florida
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    Pentair Cartridge filter, Pentair SWG, Pentair Intelliflow VS pump (11018)
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    using BBB for pool chemistry/Lamotte ColorQ tester for daily testing

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    I don't have an auto cover but I put my cover on every night, and I have noticed too in the cooler weather with less usage i have had to move my IC20 from 40% down to 20% to bring my levels down, which were hovering around 7ppm.
    If you do leave your cover on during the day(s) your chlorine with increase. You should take your cover off as much as possible even when you are not using your pool to let it breathe and disappate chlorine.

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    AZ Pool Boy's Avatar
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    Re: SWG and automatic pool cover

    Thanks, Donald.

    Quote Originally Posted by donaldm823
    My biggest benefit of the cover is that my pH stops going up!
    I wish mine would. I still have to add about 3 lbs of dry acid a week.

    Regards,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    AZ Pool Boy's Avatar
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    Quote Originally Posted by crazycanuck
    I don't have an auto cover but I put my cover on every night, and I have noticed too in the cooler weather with less usage i have had to move my IC20 from 40% down to 20% to bring my levels down, which were hovering around 7ppm.
    If you do leave your cover on during the day(s) your chlorine with increase. You should take your cover off as much as possible even when you are not using your pool to let it breathe and disappate chlorine.
    Thanks, Crazy'. Are there other benefits to letting it breathe? I think I'd rather leave the pool closed and simply turn the SWG way down, or even on a schedule where it's off most days. We live in a pretty windy/dusty area, so the cover is a godsend in keeping the sand out.

    Regards,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    JasonLion's Avatar
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    If you keep the cover on all the time there is a fair chance of CC going up. Other than that it shouldn't be a problem as long as you figure out the right percentage on the SWG. Basically if you can keep FC and CC at appropriate levels with the cover on you will be fine. If either one gets out of hand then openning the cover during the day will help.
    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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    AZ Pool Boy's Avatar
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    Thanks for the tip, Jason! I'll definitely start watching my CC.

    Regards,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    Re: SWG and automatic pool cover

    Quote Originally Posted by AZ Pool Boy
    I still have to add about 3 lbs of dry acid a week.
    Have you tried lowering the TA level (to around 70-80 with high CYA, or lower with low CYA), a higher 7.7 pH target, and/or using 30-50 ppm Borates in the pool? These methods have helped others reduce the rate of pH rise. You should also find that lowering the SWG level (on-time) results in a slower rise in pH.

    Richard
    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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    AZ Pool Boy's Avatar
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    Re: SWG and automatic pool cover

    Quote Originally Posted by chem geek
    Have you tried lowering the TA level (to around 70-80 with high CYA, or lower with low CYA), a higher 7.7 pH target, and/or using 30-50 ppm Borates in the pool? These methods have helped others reduce the rate of pH rise. You should also find that lowering the SWG level (on-time) results in a slower rise in pH.
    Richard
    No I have not, and those ideas sound very interesting. I'm still a pool noob, so have a lot to learn. It would probably help me a lot to have you smart folks on this site review my pool chemistry in general to give me any pointers. I'll get all my numbers together and report back. Maybe I should start a separate thread under the chemistry forum for this?

    Thanks a bunch.
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    Re: SWG and automatic pool cover

    Quote Originally Posted by AZ Pool Boy
    Thanks, Donald.

    Quote Originally Posted by donaldm823
    My biggest benefit of the cover is that my pH stops going up!
    I wish mine would. I still have to add about 3 lbs of dry acid a week.

    Regards,
    AZ
    And here I have always been told to Never use dry acid on a pool with a salt system

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    Yes, 1 pound of dry acid (sodium bisulfate) in 10,000 gallons adds 9.6 ppm to the sulfate level. High sulfate levels presumably have created problems with salt cells and some surfaces (plaster?), but I don't know the exact levels where such problems occur and its only been told here on the forum -- I don't have scientific sources for this, but I do know from sources on hardscape corrosion that salts of sulfate are far more destructive than salts of chloride in terms of salt crystallization pressure (so from splash-out and evaporation on hardscape surfaces).

    Richard
    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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    Quote Originally Posted by chem geek
    Yes, 1 pound of dry acid (sodium bisulfate) in 10,000 gallons adds 9.6 ppm to the sulfate level. High sulfate levels presumably have create problems with salt cells and some surfaces (plaster?), but I don't know the exact levels where such problems occur and its only been told here on the forum -- I don't have scientific sources for this, but I do know from sources on hardscape corrosion that salts of sulfate are far more destructive than salts of chloride in terms of salt crystallization pressure (so from splash-out and evaporation on hardscape surfaces).

    Richard
    Yikes. Thanks, Richard. My pool builder is the guy who recommended the dry acid. He's been in the biz for a long time, but is probably new to SWG. I love the dry acid for convenience. One big bucket lasts a long time. I dump one treatment of dry acid into a bucket, add water from the hose, then dump the bucket into the pool. That's seems a lot easier than having a case of muriatic acid around at all times, although granted the liquid acid is easier to apply. I just bought a new bucket of dry acid ($70), so maybe I'll switch over when it's empty. The only hardscape I have near the pool is the cool decking, and I try to keep the water off decking as much as possible because of all the trouble I've heard with salt attacking hardscape as well. I do have a white coating on my nice shiny blue tiles though that I'm not wild about. I guess I'm going to have to look into this some more.

    Thanks again,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

  13. Back To Top    #13
    I think the reasoning behind not using it had more to do with whatever dry acid is made of, when it passes through the electrodes of the cell the electro-chemical reaction causes a dangerous formation of explosive gas. If for some reason your salt system was powered on while your pump wasn't moving much water the gas could reach dangerous levels.

    Anything is possible though, I've even heard a rumor that smoking is bad for you.

  14. Back To Top    #14

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    Salt cells produce hydrogen gas even with no sulfates in the water. Chlorine is generated at one plate while hydrogen gas is generated at the other. You can see these hydrogen gas bubbles streaming out of a return at night if you run the pump and SWG and turn on a pool light. These bubbles are the primary source of aeration that causes the pH to rise in most SWG pools.

    I don't see how sulfates make anything more explosive. The hydrogen can build up pressure if the pump isn't on and the safety mechanisms in the SWG fail, but this will be a pressure explosion, not a chemical one. One would have to have oxygen introduced or generated, which could happen if enough chloride got used up, but that seems unlikely. Nevertheless, pressure explosions on the soft plastic of a salt cell can still seem dramatic.

    Perhaps Sean knows if sulfates are a problem for salt cells and if so why and at what levels.

    Richard
    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"

  15. Back To Top    #15
    I dump one treatment of dry acid into a bucket, add water from the hose, then dump the bucket into the pool
    Sounds Dangerous. I thought it was always add acid to water not the other way around.
    14,500 inground gunite
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    Quote Originally Posted by vegas_dp
    Sounds Dangerous. I thought it was always add acid to water not the other way around.
    Technically, you're right. However, that's more for concentrated liquid acids. The reasons are for spashing and exothermic release of heat, which can also cause splashing of acid. Neither of these seems to be a problem with the dry acid. The reason I add the water to the acid is so that the stream of water dissolves and mixes the acid. If you dump the dry acid into the water, then you need to stir it to get it dissolved. Of course you can just dump the dry acid into the pool, but it tends to bleach the plaster if it hits it. At least that's been my experience.

    Cheers,
    AZ
    13,500 gls. i/g vinyl lined pool. 13 x 32x 5
    3Bs maint. "bleach, borax,baking soda", (unless on the lazy side, then throw some trichlor pucks into the rainbow feeder.)

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    Some systems have feature built into the timer to shut off the SWG about 1 minute before the pump turns
    off, this will flush the hydrogen out of the system.

    In one pool I had, I covered it during the winter for 4 months and during that time I had to shut
    off the SWG to keep from making too much Chlorine. Since the sun's UV rays were blocked it
    couldn't eat any Chlorine.

    I suspect that with a automatic pool cover your could drastically reduce your SWG run time.
    Also, since the pool is covered most of the time the dirt and trash won't make it to the pool and this
    should allow you to reduce your filter pump run time.

    Bottom line your pool cover should reduce your pool run costs considerably.

    Cliff s

  18. Back To Top    #18

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    Sulfates are damaging to the cells. I'll try to find the electro-chemical reaction behind it.
    Sean Assam - Sean@teamhorner.com
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    Quote Originally Posted by JasonLion
    If you keep the cover on all the time there is a fair chance of CC going up. Other than that it shouldn't be a problem as long as you figure out the right percentage on the SWG. Basically if you can keep FC and CC at appropriate levels with the cover on you will be fine. If either one gets out of hand then openning the cover during the day will help.
    For what it's worth, I have an opaque electric safety cover that keeps our pool covered all the time except when we use it. I hardly measure any significant Combined Chlorine -- almost always < 0.2 ppm, the smallest measurable amount. So while in theory not letting the pool breathe can lead to a buildup of CCs, I think that unless the bather load is higher then this isn't usually a problem. When the cover is open and the pool is being used, it is usually exposed to sunlight so that combined with a typical light breeze probably has enough continual breakpoint to keep the CCs manageable.

    The chlorine usage is a significant function of how long the cover is open. My pool is manually dosed with chlorinating liquid, but the same principal would apply to an SWG. My pool uses only 1 ppm FC per day when it's in use daily and in the past when used 2-3 days per week the usage was only 0.5 ppm FC per day. I usually keep the chlorine at around 2-5 ppm FC at 20-30 ppm CYA though I plan on increasing the CYA level this next season so that the swing in FC has less effect on disinfecting chlorine. I only add chlorine twice a week during the summer. If I had the cover open all day, I'd expect the FC usage to be almost half of the FC level (so an average of perhaps 2-3 ppm per day).

    Richard
    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"

  20. Back To Top    #20

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    Quote Originally Posted by Poolsean
    Sulfates are damaging to the cells. I'll try to find the electro-chemical reaction behind it.
    As you might expect, I look forward to seeing the chemical reaction.
    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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