Calcium Cloride and Sodium Carbonate

[BradB]

This comes up a lot, but I wanted to a thread dedicated to this, as I have never seen a good answer. A lot of people suggest the importance of adding Calcium Chloride and buffer in the correct ratios.

If I add Calcium Chloride without Sodium Carbonate, the Caclium will get used as Calcium Carbonate (assuming I have enough Carbonate in the system), but where does the Chlorine go?

Similarly if I add Sodium Carbonate, without Calcium Chloride, where does the Sodium go?

Do these have to be added in precise ratios? Can we just add Calcium Cloride when Caclium is low, and buffer when PH and Alk is low?

If I am adding things to my tank over a long time (1 year) and the ratio isn't exactly right, will this cause a build-up of something I don't want?

Is there any way to test if we are doing something wrong?

 

[jdeets]

Here are a couple of articles on this subject that should give you all the information you need on this topic:

Article 1
Article 2

You are perceptive in realizing that when you use CaCl2 and sodium bicarbonate, each will have "leftover" ions. Basically, as the Ca from the CaCl2 is used up and the bicarbonate from the sodium bicarb is used up, you are left with sodium and chloride ions--or salt. Thus, your SG will tend to rise with the use of this method of supplementation, because each component leaves its "orphan" ions behind. Additionally, if you only use one and not the other, eventually you'll end up with an ionic imbalance that can wreak havoc on your water chemistry.

That's the nutshell version. The articles should give you a thorough understanding from both a chemical and practical aspect.

 

[BradB]

Great articles! but my biggest question wasn't addressed. Our aquariums contain large quantities of Na+ and Cl- ions. Does the ratio between these ions matter? What happens if I have a lot more Cl- ions than seawater, and fewer Na+ ions? Do we not test for Cl- and Na+ becuase they aren't really important, or becuase they are hard to test for?

 

[jdeets]

Na++ and Cl- ions are not tested for, directly, because they are "placeholders" in the system. You test them indirectly when you test your SG. But there is no need to test them directly. They are just constituent ++ and - ions in the solution we call seawater.

Now, suppose you end up with a bunch of extra Cl- ions that don't have enough Na++ ions to asociate with. They're going to need to associate with something. They may associate with Mg++, or with Ca++, or whatever other positively-charged ions are in solution. If you get a very large imbalance in + and - ions, you may eventually find it difficult to maintain Ca++ at any respectable level. "Ionic imbalances" as they are called can devastate your Ca level, as well as the levels of other ++ charged ions that will no longer be freely available in solution.

Not a very scientific explanation, except to say that you really never end up with "excess" ions of any kind, because they will associate with something in the solution. Depending upon what they associate with, you could see some strange things happening with levels of various biomineral components.