[APD] Re: Invertebrates and carbonates

["James Purchase" <jppurchase at rogers_com>]

Sourcing CaMgCO3 - You don't need to go buy a 50 lb bag of limestone if you
only have a few aquariums. Calcium/Magnesium supplements ought to be
available in ANY good drug store in the vitamin section. The best brands for
our purposes are the generic ones - they won't contain additives. You can
also get Iron Gluconate and Potassium tablets from the same source. I prefer
to use the CaMgCO3 over plain CaCO3 because of the presence of Magnesium in
Dolomite. While not needed in the same amount as Ca++, Mg++ is also an
essential element and if your well water is soft and mineral free, it won't
hurt to add some.

" Again -- will the calcium carbonate buffer or do I also need some other
substance?"

That depends on your water and what it contains in the first place. I
mentioned apples and oranges earlier, guess its time to further the
explanation...

We deal with two issues here, Alkalinity (Buffering Capacity) and Hardness
(the amount of divalent metal ions such as Ca++ and Mg++ in the water). They
are related mainly by the fact that they can both come from the same
original source, ie. CaCO3 or CaMgCO3, but that is the extent of the
"relationship".

Calcium Carbonate isn't very soluable in water, but it does still dissolve.
If you are supplementing CO2 in your planted tank, more CaCO3 can and will
dissolve more readily. Once it dissolves, it becomes two species of ions -
Ca++ and CO3--.

The Ca++ (and the Mg++) ions is the fraction responsible for your water's
"Hardness".

The CO3-- (as well as the bicarbonate ion, HCO3-) is the fraction
responsible for the water's Alkalinity or "Buffering Capacity"

In a planted tank, we need BOTH. Where those ions come from is secondary,
the plants don't care. In really soft water, you can get more "bang for your
buck" on the Alkalinity front by using Baking Soda (NaHCO3), as it is very
soluable in water and dirt cheap. The bicarbonate portion of the molecule
becomes the HCO3- ion when dissolved in water and is what stabilizes the pH
of the water. The Na+ ion just goes into solution and is of no concern to us
here (it does raise the salinity of the water but not enough to worry about
given the small quantity we use).

How you increase the Ca++ and Mg++ content of soft water is a matter purely
of personal preference. Since I live in an apartment and don't need a 50 lb
bag of limestone hanging around (no garden to use it in), I prefer to use
the dietary supplements I mentioned earlier. A bottle of pills takes up less
space than a bag of ground limestone. As well, my tap water comes from Lake
Ontario and is already moderately "hard" and has plenty of Alkalinity to
begin with, so for me, this whole issue is moot.

Since you are using well water, I suspect that you don't really KNOW the
exact numbers for Hardness and Alkalinity of your water as it comes out of
the tap. You can get relatively inexpensive test kits to measure both - a
Hardness Kit will give you an idea of the Ca++ content of your water and the
better kits can also separate out the Ca++ / Mg++ ions. Don't sweat it if
the kits available to you can't do this.

A KH test kit (incorrect name, but that's what they are called) will
determine the Alkalinity of your water, and let you know how much "buffering
capacity" you have. This is important if you are adding CO2. Without
sufficient buffering, you risk a severe pH drop (which can kill your fish).

So, whatever you decide to use is up to you. As long as you can get BOTH
Ca++ and CO3-- into the water things ought to be fine. However, I suggest
sticking with common chemicals and staying away from some of the more exotic
"buffers" (usually phosphate based) as those will only complicate your life.

James Purchase
Toronto



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