Removing calcium and magnesium?

[aquarium]

I think the typical whole-house water softener is rated in the 500 gallons per day range. At that rate it would take two weeks to fill a 15,000 gallon pool. Doable, but not practical.

[catnip]

aquarium, as I understand water softener operation (I've had two over the years), you should be able to operate the softener continuously until you've reach the resin bed capacity which would be around 1800 gallons for a CH of 340 ppm in a 36000 grain capacity softener. Then you regenerate the resin in the softener which takes around two hours and proceed with operation. The only caveat is that you need to make sure the salt used to regenerate the resin is totally dissolved which could take some time depending upon the type of salt you use. You can get automatic regenerators that will regenerate based on the water usage vs. timer based regeneration or manual regeneration.

So, given those capabilities, I think you could reasonably fill a 18000 gallon pool in 3 to 5 days...or faster with a high flow rate softener.

[catnip]

chem geek, would you recommend your method for reducing calcium in an entire pool vs. just fill water?

[chem geek]

Chuck,

If you are referring to my proposed method of adding Sodium Carbonate (Soda Ash) to raise TA and pH to ridiculously high levels, I would not do that in an entire pool. If you did that in a pool with gunite/plaster, you probably wouldn't just precipitate calcium carbonate, but would form scale on the plaster making the surface rough (both unpleasant and more likely to retain algae). I was proposing that this method be used in a large tub where you put your fill water and "process it" before putting it into your pool. So you would precipitate the calcium carbonate, then remove the solid (or drain the water to another tub), then lower the pH back down and aerate to lower the TA and then finally adjust the pH and put the water into the pool (sounds like a pain in the butt to me).

The water softener approach proposed by dannyboy is much more sane, but is again only practical on smaller volumes of water, so for fill water (though what you said about taking 3-5 days doesn't sound so bad, but man that's a lot of regeneration needed).

If you've already got an entire pool with high CH and magnesium and have fill water high in CH and magnesium, then there don't seem to be great choices available. One could try using either of the above two techniques on the fill water over time and replace (drain and refill) the pool water with this processed fill water.

The easiest thing to do, of course, it to just live with the higher calcium and magnesium content. To avoid scale, one would use lower than normal TA and possibly lower pH levels (say, 7.2-7.3). Having a lower TA level is actually not a bad thing since it will reduce the outgassing rate of carbon dioxide and thereby lower the rate of rise in pH and acid demand. If one wants more buffering capability, then one can add borates (about 50 ppm should do). Of course, one would still have "hard" water in terms of calcium and magnesium so the original problem of crinkly hair would probably not be solved.

Richard