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How can I chemically force the immediate precipitation of calcium carbonate in pool water? Answered

What chemical(s) do I need to add to the pool water that is safe for bathers and will force the immediate precipitation of calcium carbonate? My calcium hardness is at 2500ppm and I need to get it down to less than 200ppm. I want to precipitate out the calcium carbonate and then vacuum it out.

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lemonie (author)2009-05-29

If you increase pH, you should see it dropping out - sodium hydroxide would be an easy additive. If you're going to play with pH you should get a pH meter or at least some kit to measure it. Knocking it up a bit to 7.5 might be enough, but after you've cleaned out the lime, you'd want to take it back down again - dihydrogen phosphate, or hydrochoric acid.
(That's what I think - I've not treated pools)

L

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thematthatter (author)lemonie2009-05-30

do you know how many lbs of NaOH needed to raise the pH of a pool and how many gallons of hydrochloric acid needed to bring it back down? Might be easier and cheaper to just drain the pool and start over.

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lemonie (author)thematthatter2009-05-31

I could work it out if I knew the volume of water. With a hard-water supply draining it isn't going to improve things. L

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goodgnus (author)lemonie2009-06-08

My pool is 22,000 gallons. Where can I commonly find NaOH?

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thematthatter (author)lemonie2009-05-31

its going to make the water real salty too when your done.

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lemonie (author)thematthatter2009-05-31

I don't think so - If you've got 100 m3 of water at 2500ppm, I make that 2.5mg for each of the100,000 litres of pool water, or 250g. 250g is ~1.5 Mol of what I guess is Ca2HCO3 - requires ~26g of NaOH - not going to end up very salty.

L

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thematthatter (author)lemonie2009-05-31

26 grams of NaOH can raise the pH of pool water of 26K gallons to 7.5? Ive done these calculations in the past but haven't messed with them in 3 years.

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lemonie (author)thematthatter2009-06-01

got the sum the wrong way around - 60g. Low molecular weight, quite a lot of strong base. Anyway, I just tested this on some hard water, see above. L

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lemonie (author)2009-06-01

Hi,

In a small test on hard, hard water, NaOH does force hardness out.

L

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