09-02-2010, 07:18 PM
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Originally Posted by Byron
You cannot and should not use pure calcium carbonate as a substrate. I suspect your friend is correct, it would turn to cement or something similar. Calcium carbonate (CaCO3) is a substance found within certain rocks, shells (of marine creatures), etc. It is usually available as a powder, and used in lime for instance for gardens.
When we refer to certain types of rock (limestone, marble, dolomite), shells (of crustaceans) and coral as being calcareous, that means these materials contain calcium carbonate.
Calcium and magnesium are the two prime minerals that create hardness in water when they dissolve into it. Water running over limestone will be hard due to the dissolved calcium. In aquaria, this is fine for livebearers that need hard water, or rift lake cichlids. But in a tank of soft water fish it will work contrary to the needs of the fish.
As for substrates, speaking only from the fish aquarium perspective, I am only aware of those made with dolomite, crushed coral, marble, limestone; the calcium carbonate in these materials as I mentioned above will raise the hardness and corresponding pH of the water.
Seems to me like he's saying it'd be fine as long as your fish needed hard water?