banderbe

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!

dennis

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

http://www.aquaticplantcentral.com/f...?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.

RTR

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.

banderbe

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..

dennis

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

Salt

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.

chiahead

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.

Salt

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.



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.

Salt

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.

banderbe

Salifert makes a freshwater calcium only test kit.