Calcium Carbonate as a Substrate? - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 2 Old 09-02-2010, 08:31 AM Thread Starter
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Question Calcium Carbonate as a Substrate?

I'm posting this in both the saltwater and freshwater sections because I don't know who would be more likely to know the answer.

So there's substrate out there for reptile tanks that's called calci-sand and it's calcium carbonate. I found a page online about the dangers of over exposure harming reptiles and humans, but what about fish? I mean, there's lots of things we put in tanks that can be dangerous to us (the first that came to mind is just about every ich medication that's known to the state of california to cause cancer). So would calcium carbonate in your tank hurt your fish? Here's the link to the page on the dangers:

Calcium Sand - Dangers

So, assuming all of this is null and void because it's in a fish tank (which doesn't make a lot of sense but also wouldn't surprise me), what effect would this have on the water chemistry? Does anyone know if it would affect the amount of calcium or the pH or something in the tank?

I asked my friend and she said she had no idea about the water chemistry but when this stuff gets wet it hardens almost to a cement. If THAT is also true, what would happen if you used it like sand in your tank, stuck some plastic plants in it, and then filled it with water? Would it give you a solid substrate to hold plants in place and you wouldn't have to clean it? I know a lot of beneficial bacteria lives in the gravel/sand, but maybe a thin layer underneath would hold down your plants so your big fish (i.e. SA cichlids) couldn't "redecorate"?

I know you don't really use plants in saltwater but I figure someone out there might know about the calcium and all that, since obviously I don't.


(Sorry there's like three different questions, I was thinking really deeply into this)
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post #2 of 2 Old 09-02-2010, 01:35 PM
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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.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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