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Old 06-17-2011, 01:17 AM   #1
Nateo
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Default Estimate water profile from water softener / decreasing water hardness

Hey guys,
I understand the basics of how a water softener work. Na+ replaces Mg++ and Ca++.

I got a C- in chemistry, so give me a break for the dumb question, but if I know the water profile (how much Ca and Mg my water has before the softener), how would I estimate the water profile post-softener?

I wanna say just add up the Ca and Mg, and multiply by 2, but I think that's wrong.

If the softener strips the bicarbonate of its Ca, where does the CO3 part go?

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Last edited by Nateo; 06-18-2011 at 08:00 PM. Reason: revised title
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Old 06-17-2011, 02:08 AM   #2
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The Ca and Mg are replaced on a milliequivalent for milliequivalent basis. Ion exchange softeners are very efficient at removing nearly all divalent ions such as Ca, Mg, Fe, and Mn. So, you can use a program like the water adjustment sheet in Bru'n Water to estimate the new Na concentration.

Input your water profile information and note the milliequivalents of your cations. Then zero out the Ca and Mg concentrations and increase the Na concentration until you calculate the same number of cation milliequivalents. That is the approximate Na concentration produced by the water softener.

The concentrations of the anions are unchanged by the cationic exchange resin in the water softener. That means that the carbonate or bicarbonate concentrations are unchanged by the softening. The alkalinity is unchanged. Although the Ca concentration, the carbonate and bicarbonate are still readily paired with cations such as Na. Don't forget about sodium bicarbonate!

By the way, I saw the water profile you posted. Darn hard water!

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Old 06-17-2011, 02:11 AM   #3
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Divide calcium as mg/L by 20 or as ppm as CaCO3 by 50. This is the number of milliequivalents of calcium in the source. Divide Mg as mg/L by 12.15 or as ppm as CaCO3 by 50. This is the number of mEq/L magnesium. Add these two together. That's the total number of mEq/L calcium and magnesium removed and replace by sodium. Multiply that number by 23 to get the mg/L sodium in the processed water. Ca++ and Mg++ go to close to 0 to be replaced by Na+ as calculated above. All other ion stay more or less the same (except that cations such as iron, strontium etc will be replaced with sodium).

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Old 06-17-2011, 02:37 AM   #4
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Thanks for the quick responses guys! I just moved to a new place that has less-than-ideal water, so I'm having to re-figure all my water chemistry. The water actually tastes good, it's just problematic for brewing.

A quick google search told me that ppm and mg/l are close enough to not worry about it. Is that correct?

My Ca is 74ppm, Mg is 47ppm. 74/20 = 3.7, 47/12.15 = 3.87. Ca+Mg = 7.57. 7.57*23=174.

So my softened water has 0 Ca and Mg and 174 Na.

Is that correct?

I'm thinking of doing a 50/50 mix of softened and unsoftened water, which would sort of balance out my water decently. My unsoftened water only has 2ppm Na to begin with, so a 50/50 mix would give me 37ppm Ca, 23.5ppm Mg, and 88ppm Na, 6 SO4 and 4 Cl. The sulfate is still really low, so I don't think I should be worried about harshness from the Na, but should I be? I almost only brew low-hopped malty beers, so I thought the Na would add some nice sweetness

The bicarbonate would still be an issue, but I was planning on knocking that out with phosphoric acid.

The other thing I wanted to get a GH/KH kit and try was Kai's-via-AJ's method of slaked lime magnesium/carbonate reduction. My water is so low in everything except bicarb and Mg I think I could get some decent water that way. I don't think many homebrewers go that route. Besides Kai's website, I haven't found much info on that.

I know I could just buy RO water (which is a pain because I live out in the boonies now) or buy an RO unit, but that just feels like cheating to me, for some reason.

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Old 06-17-2011, 12:55 PM   #5
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Yes, 1 ppm is, to all practical purposes, the same as 1 mg/L but where you have to be careful in this context is that hardness can be reported "as calcium carbonate" in which case they almost always use "ppm" whereas if it is reported as the ion it is almost always "mg/L". If you see the words "as CaCO3" then you are sure.

Assuming that the calcium and magnesium numbers are mg/L as the respective ions then the numbers look right. As the exchangers aren't 100% efficient you will still have a mg/L or so of each of Ca++ and Mg++ and, correspondingly less Na+.

The blend should split the differences but why not just brew with the water as is and blend with RO if you need to control alkalinity. Remember that if you do that with phosphoric (or any other acid) you are swapping each bicarbonate ion removed for phosphate ions. Unless the alkalinity is out of sight this is pretty decent water.

Decarbonating by lime treatment or boiling is a lot more trouble, IMO, than just diluting with RO, is a bit iffy (i.e. you don't get the same result every time) and really requires the use of a pH meter to do properly.


Guess I don't understand why RO is cheating any more than ion exchange.

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Old 06-17-2011, 01:21 PM   #6
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Just for reference, here is the water profile Nate posted on the AHA forum.

Sodium, Na 2
Potassium, K < 1
Calcium, Ca 74
Magnesium, Mg 47
Total Hardness, CaCO3 381
Nitrate, NO3-N 0.5 (SAFE)
Sulfate, SO4-S 2 (6ppm)
Chloride, Cl 4
Carbonate, CO3 < 1
Bicarbonate, HCO3 440
Total Alkalinity, CaCO3 360

Darn hard and alkaline. Extremely suitable for lime softening excepting that he should not be following Kai's or AJ's advice on the methodology. The high Mg content should also be addressed by performing an Excess Lime treatment. The main difference from what Kai and AJ recommend is that the pH MUST be increased to at least 11 in order to precipitate the Mg along with the Ca.

Although AJ and I appreciate the simplicity of using our own RO systems, that is an investment in the hundreds of dollars. That compares to the investment of about $6 for the lime needed to treat thousands of gallons of water, and the cost of an acid and a pH meter. RO is nice, but in this case a much cheaper alternative exists if Nate doesn't want to go that route.

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Old 06-17-2011, 03:17 PM   #7
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Readers will have to decide themselves whether to use my method or not so lets just be clear on what my method is. It is a modification of the traditional 'split' treatment.

1. Calculate how much lime is needed to drop all the calcium and magnesium
2. Add this much to the whole volume of water (this is a difference WRT the split method).
3. Check pH. Continue to add lime until pH is 11 or a little over. This will cause both CaCO3 and Mg(OH)2 to precipitate.
4. Decant off the precipitate.
5. Add a bit of chalk to the clear water and get it into suspension. Just a smidgeon - it's only there to provide nucleation sites.
6. Bubble air or CO2 through the water while monitoring pH. Eventually it will get back into the eights or even lower depending on how long you are willing to wait. Be prepared to wait quite a while. When the pH is below 8 you are finished.

Where this differs from the traditional split treatment is in the way the excess Ca(OH)2 remaining aftger Step 4 is dealt with. Depending on how much lime you added the pH may fall back as the CaCO3 precipitates. If it does you haven't added as much as you need to get all (or as much as possible) of the magnesium. So if you've done it right the pH should be near 11 at the completion of precipitation and there will be excess Ca(OH)2 which is a base and must be neutralized if you don't want it contributing to the alkalinity of the water. You undertook this process to reduce alkalinity. In the traditional split treatment one third of the water is held back (the lime is added to 2/3) and the acid used to neutralize the (OH)- ions is the bicarbonate ion (HCO3-) in the reserved 1/3. The problem is, of course, that you don't get the magnesium (or much of it) in that 1/3. This is, in many cases, fine but if you want to get as much as you can then you'd have to use my method or something like it. In my method we're using carbonic acid, a stronger acid than bicarbonate ion, to do the neutralizing:

Ca++ + 2(OH)- + H2CO3 ----> CaCO3 + 2H2O

One can, of course, use any acid (well obviously nitric and prussic wouldn't be good choices) bearing in mind that the neutralized hydroxyls are being replaced by the anion of the acid

Ca++ + 2(OH)- + H2SO4 --> 2H2O + Ca++ + SO4--

In a case such as the water in question the sulfate and chloride are low and use of sulfuric or hydrochloric may be reasonable approaches. Of course carbonic acid is free if you take it from the air. Your cost will be time.

If ever I saw a case for an RO system, this gentleman's case is it. I do, however, appreciate that peoples budgets and approaches.... are different. One can also learn a lot of water chemistry by following the method I've outlined and trying to understand it.

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Old 06-17-2011, 04:51 PM   #8
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AJ, that's odd that you say this water is better suited to RO since it has very low permanent hardness and very high temporary hardness. Lime softening will produce a ending Ca content in the 30 ppm range and Mg content in the 10 ppm range. Pretty good result in my opinion. The only thing not adequately addressed is the alkalinity. That is what acid is for.

PS: for a water this hard, it is best to feed an RO system with the water from the ion-exchange softener. That will greatly extend the life of the membrane.

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Old 06-17-2011, 05:35 PM   #9
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Sorry, I should've posted the whole water report first so you'd know what I was talking about. Thanks Martin for reposting that for me.

I completely agree that buying an RO unit or RO water would be the easiest and most convenient (though you could make the same argument for buying beer vs making beer), but I like tinkering, and although I don't know much about chemistry it's something I want to learn more about.

I just bought a new kettle, burner, MLT, digital pH meter, and some other odds and ends while I was waiting for my water report to come back, so my brew budget is kind of shot for a while, so an RO unit, if I go that route, will have to wait.

Thanks so much for you guys holding my hand through this. I was planning on using phosphoric acid to neutralize the alkalinity because of the amount of phosphate already in the malt. Is that a reasonable approach? I don't have any hydrochloric acid on hand, though I could probably find some.

I'll be getting a GH/KH test kit soon so I'll be able to do some experiments.

Thanks again for all your help. This is an interesting area of brewing that has very little info available in the homebrew world.

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Old 06-17-2011, 07:24 PM   #10
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Quote:
Originally Posted by mabrungard View Post
AJ, that's odd that you say this water is better suited to RO since it has very low permanent hardness and very high temporary hardness. Lime softening will produce a ending Ca content in the 30 ppm range and Mg content in the 10 ppm range. Pretty good result in my opinion. The only thing not adequately addressed is the alkalinity. That is what acid is for.
The alkalinity is huge and its hard to predict exactly what will happen with lime treatment. Done right he ought to be able to get much of the magnesium and assuming the usual 1 mEq/L rule of thumb the alkalinity and calcium down to around 50 ppm as CaCO3 each. So what I meant was, and I mentioned it because of his statement that he didn't want to do RO, if anyone would benefit from RO, he would. I certainly wouldn't want to have to deal with the lime treatment each time I brewed and I wouldn't feel comfortable without doing an analysis for each treatment.
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