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

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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lemonie8 years ago
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)

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.
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
goodgnus (author)  lemonie8 years ago
My pool is 22,000 gallons. Where can I commonly find NaOH?
its going to make the water real salty too when your done.
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.

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.
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
lemonie8 years ago

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