# Confused about GH, Mg, Ca



## banderbe (Nov 17, 2005)

I am trying to understand precisely what 1 degree General Hardness means.

I know it is a measure of positive Ca and Mg ions, and I know it is represented as CaCO3.

What I do not understand is if there is always a fixed ratio of Ca to Mg in 1 dGH, or if 1 dGH can be made up completely of Mg, or completely of Ca.

I ask these questions in light of my results from the Aquarium Pharmaceuticals GH test kit which says I have 5 dGH, and in light of the fact that my water passes through a home water softening unit that says it exchanges Ca ions with Na ions.

I want to know if I have any Ca whatsoever in my water. If there is a fixed ratio of Ca to Mg in 1 dGH then I do have Ca and can calculate how much based on the known ratio.

If there is no ratio then I cannot know, save for a test kit, how much Ca I have in my water.

Ultimately I want to know if I need to dose Ca (and/or Mg).

Anyone who *knows* the answers to these questions, please help me out!


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## dennis (Mar 1, 2004)

First, see this thread, especially the last 2 pages.

http://www.aquaticplantcentral.com/forumapc/showthread.php?t=9519&page=5

In a perfect world GH measurments are teh combined total of a ratio between Ca and Mg of 4.1 However, in the real world your GH can be made up of any ratio between Ca and Mg, as well as other salt ions like Na, K, etc. You coul dhave 100% Ca in your water or 100% mg or some combination of any of the above elements. The only way to determine your Ca and Mg readings are to test Gh, test Ca adn then use the formula you'll find in the link I provided you.

I would not use teh water through the softening system. Definately not. There should be water source before softner, if there is not then I would add one. Softners replace the Ca with either Na or K, usually, in your case Na. Na in more than trace amounts is harmful to your plants and possibly to your fish.


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## RTR (Oct 28, 2005)

I though that GH only read divalent ions, not the monovalent such as Na+, K+ ? That would be a huge error source and is contrary to my experience.


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## banderbe (Nov 17, 2005)

dennis said:


> First, see this thread, especially the last 2 pages.
> 
> http://www.aquaticplantcentral.com/forumapc/showthread.php?t=9519&page=5
> 
> ...


Thanks for the link, I will check it out. As for my softened water, I guess that's up for debate as I have seen other people say it shouldn't be a problem. I am however looking into RO in the future, because if I do have a water source before the softener it's also before the water heater and thus I would have to warm it in a rubermaid trashbin or something..


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## dennis (Mar 1, 2004)

RTR said:


> I though that GH only read divalent ions, not the monovalent such as Na+, K+ ? That would be a huge error source and is contrary to my experience.


RTR,

Your absolutely right. I don't know what I was thinking but thank you for catching that. I'll go correct my post now before it messes anyone up.

banderbe,

RO would be an option for you or you could setup the the tank with hardplumbing to a water suppy and a drain, then all you have to do is open a valve, drain 10-20% then close that valve and open the other to refill. Changing that smaller amount should not cause anough of a temp change to matter and you can add a Ccapful of prime while filling to neutralize and clorine/amine.

Remember that in nature water temps can drop a lot after large rains so some temp. fluctuation is perfectly fine.

Dennis


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## Salt (Apr 5, 2005)

banderbe said:


> What I do not understand is if there is always a fixed ratio of Ca to Mg in 1 dGH, or if 1 dGH can be made up completely of Mg, or completely of Ca.


GH tests are EDTA chelation tests. Calcium and Magnesium cations react the same on these tests. No, there is no fixed ratio of Ca to Mg in 1 dGH. If it is made up completely of Mg or completely of Ca, it will read the same on a GH test. If you do a test on tap water, there is no way of knowing how much is Mg and how much is Ca unless you test using an ion selective probe or have your water company test it for you using whatever method they use.

My understanding is water softeners that use table salt (sodium chloride) exchange calcium and magnesium ions with sodium ions. I don't like them because they don't actually _remove_ ions, just exchange them, so they produce water very rich in sodium.

I don't know of any calcium test kits that only test for calcium and not magnesium at the same time. American Marine developed a "dip and read" ion selective probe meter for calcium. However, it costs $250, and is really aimed more at reef tanks (i.e., tanks with very high calcium levels). Usually ion selective probes need to be used with ionic strength adjusters (and sometimes pH adjusters) so I'm not sure how American Marine got around this. I have to admit if you gave me an ion selective Ca probe, meter, and ionic strength adjuster, I would have no idea how to use it. I sure would like to learn but my Google searches haven't turned up anything I can make sense out of.


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## chiahead (Dec 18, 2004)

Salt said:


> My understanding is water softeners that use table salt (sodium chloride) exchange calcium and magnesium ions with sodium ions. I don't like them because they don't actually _remove_ ions, just exchange them, so they produce water very rich in sodium.


Actually this is not true. Technically the tap water enters the water softner and passes through a bed of resin. The resin absorbs minerals, or whatever else they design the resin to absorb. It actually removes them from the water. The NaCl comes from the fact that the resin cannot just absorb the minerals with out some sort of cleansing.  They use the NaCl to perform 2 jobs, to flush the resin out, and to recharge or revive the resin itself. Similar to those softner pillow people can put in there filter. They recharge the same way, with salt of some kind. Sorry I am being technical, but I work with these daily. Also, a potassium based softner system would be a better choice.

Also, I do not think a RO system would remove the NaCl from the softner if you plan to use it after the softning system. I havent tested this but either way I think the added NaCl would be rough on the membrane. Just trying to help! Sorry if I stepped on some toes.


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## Salt (Apr 5, 2005)

chiahead said:


> Actually this is not true.


Um, yes it is. It's an ion exchange resin that exchanges Ca2+ and Mg2+ ions with Na+ ions. The sodium chloride recharges the resin. Unless (as you mentioned) it's a potassium softener, then it exchanges them for K+ ions.



RTR said:


> I though that GH only read divalent ions, not the monovalent such as Na+, K+


It does, but the monovalent ions can skew the results if there are enough of them. Lamotte states in their hardness kit instructions to dilute a saltwater sample by 92.25%. Personally, I used to maintain a .10% salt level in my tank (1000 ppm NaCl). I recently stopped. As I did weekly 40% water changes and the NaCl dropped, I noticed that I was having to add more Ca and Mg to get the same test kit readings. It ended up I had to add 84% *more* Ca and Mg to remineralize my RO/DI water and get the same test kit results *after* NaCl levels dropped to negligible levels.

I also need to correct myself regarding my statement that I don't know of any kits that test only for calcium. Lamotte makes one, test kit #3609. It includes inhibitors that stop ions other than Calcium from registering.


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## Salt (Apr 5, 2005)

chiahead said:


> Also, I do not think a RO system would remove the NaCl from the softner if you plan to use it after the softning system.


I'm not sure why you would think that. The water softening system does not add NaCl, it exchanges calcium and magnesium ions for sodium ions. It would work the same as it would with his untreated tap water.


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## banderbe (Nov 17, 2005)

Salt said:


> I also need to correct myself regarding my statement that I don't know of any kits that test only for calcium. Lamotte makes one, test kit #3609. It includes inhibitors that stop ions other than Calcium from registering.


Salifert makes a freshwater calcium only test kit.


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## RTR (Oct 28, 2005)

Salt based water softeners must charge-balance. If a Ca++ ion is taken up by the resin, two Na+ or K+ ions must be lost to the solution from the resin. So home water softeners *do* contribute sodium (or potassium) ions to the solution - the water passing through. "Salt" is correct on this point.

Even acid-base exchange resins must charge balance. But they contribute only H+ and OH- ions to the solution (net effect is HOH = H2O) so do reduce the TDS of the solution. Exchange resins based on salt exchange increase the TDS by having to use monovalent ions to replace divalent ions.


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## dennis (Mar 1, 2004)

Re-birth!!!

Question on this "Salt based water softeners must charge-balance. If a Ca++ ion is taken up by the resin, two Na+ or K+ ions must be lost to the solution from the resin." If I test my unsoftened water's GH, then test the softened water's GH, would the difference tell me how much Na was added to the softened water?

Example, well water GH=12degrees or 214.8ppm, softened water GH=3 degrees or 53.7ppm. Subtracting those equals 161.1ppm loss. If 2 Na are added for every Ca/Mg lost, then that means you have added 322.2ppm Na?

Am I thinking about this correctly?


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## Jimbo205 (Feb 2, 2006)

If I wasn't confused about GH, Mg, Ca before, I sure am now!


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## hoppycalif (Apr 7, 2005)

dennis said:


> Re-birth!!!
> 
> Question on this "Salt based water softeners must charge-balance. If a Ca++ ion is taken up by the resin, two Na+ or K+ ions must be lost to the solution from the resin." If I test my unsoftened water's GH, then test the softened water's GH, would the difference tell me how much Na was added to the softened water?
> 
> ...


Isn't GH expressed in ppm equivalent of Calcium ions? So, if the GH drops by 100 ppm, that may be a combination of Calcium and Magnesium, with a weight equivalent to 100 ppm of Calcium. Therefore, wouldn't the ratio of atomic weights of sodium and calcium enter into that somehow? If one only wanted a rough approximation I think your calculation would be close enough.


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## dennis (Mar 1, 2004)

True, your point is good. Typical GH tests measure the total Ca and Mg (plus others if the levels are high enough) as a CaCO3 equivilant.

Last night I measured my kH (not that it matters here) of the presoftened water: kH 4.5degrees or 80pm. I also measured the Ca (lamotte kit): 310ppm as CaCO3. That means my actual presoftened Ca levels are 124ppm. (Ca is 40% of CaCO3 so 310*.4=124ppm). Softened water has a Ca of 0ppm. I need to pick up a new GH test today but my area seems to run on average 3:1 Ca:Mg so I could roughtly assume for now that Mg levels would be 41ppm.

If I remember correctly, PPM to Degrees is factor of 17.9. However, I can't remember if that is elemental or based on the CaCO3 equivilant? If based on CaCO3, then I have 17.3 degrees GH just from Ca. So, I would say that conservetivly I have a GH of 20.


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