Removing calcium and magnesium?

[aquarium]

Is there a relatively safe way to precipitate calcium and magnesium out of the water? My fill water is very high in both and I think it's causing the girl's hair to get more and more 'crinkly' as time goes by and evaporation causes the pool water to become more and more concentrated.

[chem geek]

If you add Sodium Carbonate (typical pH Up or Soda Ash or washing soda) you can raise the TA and pH which will add carbonate to the water and (along with the higher pH) will precipitate out calcium carbonate. With enough carbonate you can even precipitate magnesium carbonate though it is about 10 times more soluble.

Adding just 1 ounce (weight) of Sodium Carbonate to 100 gallons of water will make the equilibrium of calcium carbonate out of balance by a factor of 45 which should precipitate over 90% of the calcium. You might also precipitate half of the magnesium. This assumes you get the pH over 9 (which will happen unless your water has over 100 TA to start with).

Of course, you'll then be left with water with high TA, but you know how to handle that. Using Ben's procedure of adding acid and aerating, you can get rid of the excess TA. Adding 1 ounce of Muriatic Acid will bring you back down to 7.5 pH, but your TA will be higher by about 35.

Then you'll be left with salty water (Sodium from the Sodium Carbonate and Chloride from the Muriatic Acid). Just with adding what I described above, your TDS in this make-up water goes up by 100. It will go up even more with the acid/aeration process, but I can't tell how much since it depends on how efficiently you aerate.

Well, you asked! Sorry I don't know of a cleaner method.

Richard

[dannyboy]

I use a water softener to remove calcium. It also removes magnesium and
iron to a lesser extent.
I recirculate my water thru it when necessary to maintain 150CH
My fill water is over 500CH and over 300 TA.
What I know for sure is that it works. It raises my salt level and I think my
TA goes down a bit and PH up a bit. I was not to specific about before and
after measurements.
I have not seen much for discussion on the use of water softeners on this
forum.
I hope the CHEM GEEK will follow on and give us the break down of what
the water softener removes and adds to the pool and its possible effects.

[chem geek]

A water softener is just an ion exchange material (typically in the form of beads) so it will accept certain ions, calcium and magnesium which form the basis of "hard" water, and release sodium and/or potassium ions in their place. If this is all that it does, then it should lower CH, but everything else should stay the same (pH, TA, etc.). TDS (in ppm) would actually go down if Calcium were traded with Sodium (which has a lower molecular weight and is singly charged).

This is a good idea that I didn't think of. I just don't know how economical it would be for volumes of water in a pool. When a water softener cartridge gets filled up with magnesium and calcium, you replace [EDIT] or regenerate [END-EDIT] the cartridge, so they are typically rated in terms of how many gallons of water at a certain hardness they can filter. It's the best idea proposed so far, however, for reducing calcium and magnesium and I'm really glad dannyboy thought of it. Clearly for fill water, it is very economical -- I'm just not sure how much it would cost to filter your entire pool if you've already got high CH in it.

Richard

[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.

[dannyboy]

The short story is I did not have a choice. My PH always 7.2-7.8 PS233
With 300 TA and 500 CH my brand new pools sand filter after 8 # dichlor
from the pool builder turned into a brick. I had to chisel it out with a hammer.
This sites removing ALK solved 1/2 of my problem. However my good mornig
precipitate covering the bottom of my liner was only 2/3 eliminated.
A 30000 grain water softener and a shallow well pump total $600.
I cycled the water from the pool thru the system continuously. 35K gallons
9 days 36 manual reginerations later. I have got TA=110 CH=150
It used 5 bags of salt.
Some where about CH=300 all the scale and precipitate disolved and went
away.
My CH slowly goes up with fill water and I repeated the water softener
for 4 days this year. However my TA does not go up. I was curious about
that untill I read the CHEM GEEKS relative out gas rates.
Overall the water softener works for me.
My first salt reading 3 weeks ago from a talor kit was 1200. With 1 year old
water this had to come from bleach and the water softener.
I just installed 2 aquarite SWG that are working flawlessly.

[mbar]

Thanks for posting this method. It is great to have someone share what works for them, it is how we all learn That is what I love about this forum, you can learn so much from the experiences of others!

[catnip]

Richard, a question on CA (I think) percipitate which I hope you can help me with:

I'm stuck with using a pool service since we are absent from our pool for three weeks out of every four. I've been experimenting with the BBB method during the week I'm here, but the pool service uses Tri-Chlor pucks in an in-line feeder and shocks with Cal-Hypo, sometimes at high levels because we have had recent pool flooding and black/mustard algae problems. We've had to do a lot of vacuuming to waste to get rid of the dirt due to flooding...also used some floculant to settle out the dirt. The pool has been flood/dirt free for a month, but the algae is persistent on the shaded side of the pool...not terrible but clearly there.

After the most recent shock with 4 lbs. of Cal-Hypo, the pool went from very clear to moderately cloudy blue for around 12 hours and then fairly clear after 24 hours and eventually very clear. However, there was a residue of what looked white powder scattered around the bottom. The Polaris sweep moved it around but it settled fairly quickly, kind of like very fine snow flakes. Does this sound like calcium carbonate percipitate? Or could it be dead algae (though the quantity of white power seemed much greater than the relatively small amount of visible algae we brushed off)? I vacuumed the white residue to waste and otherwise the pool looks great now.

Here are the numbers:
Volume - 18,000 gal.
FC - ~20 drifting down to 3-6 after shocking with Cal-Hypo and using bleach to maintain.
CC - can't measure but latest pool store LaMotte test showed 0
pH - 7.8 reduced to 7.6 with 14 oz. of muriatic acid
TA - 75
CH - 375
CYA - 30

Thanks for your thoughts on this.

[chem geek]

After the most recent shock with 4 lbs. of Cal-Hypo, the pool went from very clear to moderately cloudy blue for around 12 hours and then fairly clear after 24 hours and eventually very clear. However, there was a residue of what looked white powder scattered around the bottom. The Polaris sweep moved it around but it settled fairly quickly, kind of like very fine snow flakes. Does this sound like calcium carbonate percipitate? Or could it be dead algae (though the quantity of white power seemed much greater than the relatively small amount of visible algae we brushed off)? I vacuumed the white residue to waste and otherwise the pool looks great now.

With your numbers, you aren't severely over-saturated with calcium carbonate in your pool even at a pH of 7.8 while at a pH of 7.5 you are perfectly fine. So I do not believe the precipitate is calcium carbonate. Yes, dumping Cal-Hypo can produce some solids just as dumping some Sodium Carbonate (Soda Ash) can do the same (I've seen the latter myself), but this is pretty obvious clumps and even these tend to dissolve over time.

You can fairly easily determine if the stuff is calcium carbonate by taking some of it (scooped up) and putting it into clean water (tap water is OK, so long as it isn't really high in CH and TA). If the stuff dissolves (give it some time), then it is probably calcium carbonate; if it doesn't, then it could be algae.

Richard