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Thread: Using Lime to soften pool water.

  1. #1
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    Using Lime to soften pool water.

    I've been reading about the use of Lime to soften water. It appears that you can add lime to water as a flocculate to precipitate out calcium. I found this paper here:

    http://www.ceegs.ohio-state.edu/~lweave ... tening.pdf

    That discusses the use of lime to soften river water. It appears that you add the lime, the calcium will then settle to the bottom, then I would think you could vacuum to waste. or filter it out. If you had a centrifuge I guess that could be used to separate it out also.

    Has anyone seen/heard of this for pools?

    I've considered doing the lab described in the paper above using my pool water in the beakers instead of the river water to see what happens. As my fill water is both high in calcium hardness and alkalinity I've been looking for something that I could use to reduce the hardness as replacing the water does not help me.
    15,500 gal, inground gunite pool with 7 ft spa, 2 speed pump 2hp/.33hp, 3/4 hp booster pump, Intermatic P1353 timer, AutoPilot SC-48, Sand filter with ZeoBest, Heater, that I never use . . .

  2. #2
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    Re: Using Lime to soften pool water.

    Quote Originally Posted by lovingHDTV
    I've been reading about the use of Lime to soften water. It appears that you can add lime to water as a flocculate to precipitate out calcium. I found this paper here:

    http://www.ceegs.ohio-state.edu/~lweave ... tening.pdf

    That discusses the use of lime to soften river water. It appears that you add the lime, the calcium will then settle to the bottom, then I would think you could vacuum to waste. or filter it out. If you had a centrifuge I guess that could be used to separate it out also.

    Has anyone seen/heard of this for pools?
    Yes, many people do this by accident when they add a baking soda or soda ash to a pool with high calcium and the water clouds from the precipitation of calcium carbonate. The problem is filtering it out which is often problematic.

  3. #3
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    Re: Using Lime to soften pool water.

    I guess what I saw as different is that it speaks of allowing the floc to settle to the bottom of the beaker. When a pool goes cloudy due to the addition of baking soda, will it also settle to the bottom so that it could be vacuumed out?
    15,500 gal, inground gunite pool with 7 ft spa, 2 speed pump 2hp/.33hp, 3/4 hp booster pump, Intermatic P1353 timer, AutoPilot SC-48, Sand filter with ZeoBest, Heater, that I never use . . .

  4. #4
    Administrator JasonLion's Avatar
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    Re: Using Lime to soften pool water.

    Calcium clouding in a swimming pool usually involves particles so small that they stay suspended and the filter can't filter them out. Obviously there is a way to get calcium to settle out and not scale, since Calsaway does that, but their process is patented. I wonder how the process in this paper compares to what they do?
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  5. #5
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    Re: Using Lime to soften pool water.

    All they are really doing is raising the pH to produce 'scale'. Lime has a high pH and by increasing both pH and calcium by adding it they insure that precipitation will occur. They state that Also, they make reference to 'carbonate hardness'. This is just another name for TA. The also say that the high pH after the process need to be neutralized with acid.
    The use of lime water (Kalkwasser) in reef aquariums is common practice to increase calcium levels but it does cause the calcium to precipitate out and the carbonate hardness (TA) to drop (which then needs to be raised with a baking soda/washing soda mixture) and coat everything with calcium carbonate. This is a problem because in a reef aquarium high calcium levels and high carbonate hardness are needed so it becomes a catch 22 situation It has a tendency to cloud the aquarium and then the calcium settles out but it does not filter out effectively, even with DE filtration. Calcium deposits also need to be scraped from the glass walls of the tank. I know this from experience. I a pool it would probably deposit scale on the pool walls.

    The commercial processes that filter out the calcium carbonate use special filtration methods that are not available to the average pool owner. While this looks interesting on paper I don't think it is a practical solution for the average pool owner.

  6. #6
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    Re: Using Lime to soften pool water.

    Several years ago I designed and built the control system for a water treatment plant that used lime softening. Quick lime is "slacked" with water (mixed in a special mixer). This process produces a large amount of heat so beware. The slurry is then pumped into a large funnel shaped separator called the Lime softener. Alum and a polymer were also injected to promote flocculation. The water was introduced into the lime softener in a manner that it circulated in a circular manner. I was told by the supplier of the lime softener that the softening process takes place along the surface of the funnel. When the water reaches the top, the floc moves toward the center of the structure, and the clean softened water exits out via a slot in the side. The floc settles to the bottom center of the lime softener, which is then pumped out periodically. CO2 is added to the water exiting the softener to lower the pH. It is then filtered via sand and activated carbon filters and then pumped out to the city. Capacity of this plant was about 10 million gallons per day.
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  7. #7
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    Re: Using Lime to soften pool water.

    Quote Originally Posted by dschlic1
    Several years ago I designed and built the control system for a water treatment plant that used lime softening. Quick lime is "slacked" with water (mixed in a special mixer). This process produces a large amount of heat so beware. The slurry is then pumped into a large funnel shaped separator called the Lime softener. Alum and a polymer were also injected to promote flocculation. The water was introduced into the lime softener in a manner that it circulated in a circular manner. I was told by the supplier of the lime softener that the softening process takes place along the surface of the funnel. When the water reaches the top, the floc moves toward the center of the structure, and the clean softened water exits out via a slot in the side. The floc settles to the bottom center of the lime softener, which is then pumped out periodically. CO2 is added to the water exiting the softener to lower the pH. It is then filtered via sand and activated carbon filters and then pumped out to the city. Capacity of this plant was about 10 million gallons per day.
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