Raising both KH & GH - The Planted Tank Forum
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post #1 of 3 (permalink) Old 05-04-2015, 04:07 AM Thread Starter
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Raising both KH & GH

Is it true that calcium carbonate (CaCO3) raises both GH & the KH? I read somewhere that by adding 2 teaspoons of CaCO3, it will increase the hardness of 50 liters of water by 4 dKH and 4 dGH.
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post #2 of 3 (permalink) Old 05-04-2015, 05:02 AM
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Calcium carbonate comes in may forms, some might dissolve relatively easily, but most will only slowly dissolve. I find that even a good GH booster takes at least a day to dissolve, and I don't add much - less than a teaspoon in a 65 gallon tank. This is not a problem, but a good feature, since it makes it difficult to too quickly raise the GH.

A teaspoon of CaCO3 cannot raise the GH and KH by equal amounts, because the atomic mass of Ca is 40 and that of CO3 is 60, so the increase in KH should be about 50% more than that of the GH.

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post #3 of 3 (permalink) Old 05-04-2015, 12:36 PM
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GH is a measure of calcium and magnesium. Anything that will dissolve in the water and contains either or both will raise the GH.

KH is a measure of carbonates and bicarbonates. Anything that will dissolve in the water and contains either or both will raise the KH.

As Hoppy notes, some materials dissolve better than others.
The finer the material the faster it will dissolve: Coral sand is faster than a chunk of coral, for example.

Here is how I do this:
1) Use Seachem Equilibrium for GH. It is a combination of calcium, magnesium and potassium. Set that where I want it when prepping new water for a water change. Shake this in a jar of water to dissolve, and it may take a few refills of the jar to dissolve it all.
2) Use potassium bicarbonate or sodium bicarbonate (baking soda) for KH. Easily dissolves.

3) Keep coral sand, oyster shell grit (sold for caged birds) or a limestone based material in the filter. (I use nylon stockings as media bags) This acts very slowly, and is just enough to stabilize the GH and KH.
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