Is CaCO3 a Good Source of Calcium? - The Planted Tank Forum
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post #1 of 43 (permalink) Old 06-26-2016, 09:13 PM Thread Starter
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Is CaCO3 a Good Source of Calcium?

My local water quality report states our water has an average of 119 mg/l CaCO3. It then reports the Calcium content to be 29 mg/l Ca. Diana says plants need 49 mg/l Ca. If that is true then the water here is Calcium deficient. What I don't understand is how water with 119 mg/l CaCO3 could be Calcium deficient.

So I've been adding about 5/16 tsp Equilibrium a week to my 20 gallon tank at 50% WC and my GH is 7 dGH. But according to my sometimes miscalculated calculations I'm still going to be a little short on Calcium even if I increase the Equilibrium by 50%. I hesitate to add more because I don't want a ton of Potassium and Sulfate. One thing I'm considering is dosing with Calcium Nitrate instead of Potassium Nitrate.

I thought CaCO3 was a source of Calcium. How can water with Calcium Carbonate be Calcium deficient?
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post #2 of 43 (permalink) Old 06-26-2016, 10:59 PM
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Hi Savetheplants,

CaCO3 (limestone) is insoluble in water unless there is excess free CO2. If there is free CO2 then the equation becomes:
Quote:
CaCO3 + H2O + CO2 = Ca+2 + 2HCO3
which is basically calcium and biccarbonate and the resultant water has increased alkalinity, pH and hardness.
However, once the excess CO2 is removed the Ca+2 reverts back to CaCO3 (insoluble limestone).

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post #3 of 43 (permalink) Old 06-27-2016, 03:17 AM Thread Starter
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Thank you for explaining this. Last time I checked the CO2 bubble count on my 20 gallon tank was 144 bpm and the pH was 7 which with 6 dKH indexes an estimated CO2 content of 18 ppm. The water report says there is 29 ppm of Calcium in the water plus I'm getting whatever my CO2 injection provides. I looked into the Calcium Nitrate since I posted and found that it is 25% Calcium so that would only increase Calcium by about 2 mg/l Ca per 1/8 tsp dose or 6 mg/l Ca a week in my case. (4,600 mg/tsp divided by 8 x 0.25 divided by 68 liters is 2 mg/l Ca) That's not much but it would be something. I'm not above throwing in some Calcium Chloride although I find that solution inelegant. I'm definitely going to increase the Equilibrium dose to .45 tsp a week at water change. (4,700 mg/tsp Equilibrium x 0.45 tsp x 0.08 Ca content divided by 68 liters is 2.5 mg/l Ca plus 50% of what was leftover before the water change.) That's not very much more Calcium. I could always crank up the CO2 gas but one of my fish seems distressed by it. He hides out on the side away from the influent trying to avoid it. I'm also looking into getting a LaMotte Calcium test kit.
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post #4 of 43 (permalink) Old 06-27-2016, 03:41 AM
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Hi Savetheplants,

I don't know if you saw the thread by Niko about using dolomite in an aquarium as a source for Ca and Mg in our aquariums. The thread, and a second thread about the dosing, caused a stir here on TPT a few weeks ago........not so much about the chemistry but the way it was presented.

Long story short I have been doing some research and dusting off the antique chemistry neurons in my old brain and there is something interesting about it. Dolomite, CaMg(CO3)2, breaks down into Ca+2, Mg+2, and HCO3 in the presence of free CO2 molecules. Both Ca+2 and Mg+2 are readily utilized by plants in the photosynthesis process (as opposed to Ca and Mg in other forms). In addition, I was reading that the HCO-3 (bicarbonate molecules) can be utilized by aquatic plants as an additional source of carbon (a key building block in photosynthesis) along with the CO2 molecules that we all know about. I just finished the second week of my experiment using dolomite instead of the Equilibrium, CaCl2, and MgSO4 that I was dosing as my sources for Ca and Mg (I have very soft water here in Seattle). So far it is too soon to draw a firm conclusion but I can say I believe I am noticing a difference. I have been keeping a log and just posted my first entry in a thread where I will document my results and conclusions.
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post #5 of 43 (permalink) Old 06-27-2016, 05:39 AM Thread Starter
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The new growth on my Anubias is yellow with thin stems. I'm getting holes in the old leaves. I used to get little holes in the tips of new leaves but that stopped when I started adding GH Booster. I'm also getting brown algae on old leaves but that's a different story. These are old Anubias that languished for several years. The Wisteria seems a little yellow to me. The Java Fern is doing nothing (good work Java Fern). Most of the plants are pearling.

I saw Niko's post. It does seem to be an elegant solution. That is to say you get just what you need out of it. But calculating the dose seems to be more involved. I have to admit I got lost along the way reading it. Not to say there was anything wrong with the presentation. That I wouldn't know.

EI says to dose 1/2 tsp GH Booster for a 20-40 gallon tank once a week at water change. I was dosing a rounded 1/4 tsp because that's what you dose for a 10-20 gallon tank. I won't get much more Calcium out of 1/2 tsp and I'm not going to use more than that.

I wonder how much Calcium gets freed from Calcium Carbonate by CO2? I mean does 19 ppm CO2 give you an extra 20 points worth of Calcium like I think I need?
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post #6 of 43 (permalink) Old 06-28-2016, 05:06 PM
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CO2 in water should not chemically combine with anything except for the small portion that becomes carbonic acid, H2CO3, which exists in the water as ions, H+ and CO3--. Calcium can combine with carbonic acid to form CaCO3, which also exists in the water as ions, C1++ and CO3--.

This is Chemistry, as taught by a non-chemist!

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post #7 of 43 (permalink) Old 06-28-2016, 05:13 PM
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Quote:
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I wonder how much Calcium gets freed from Calcium Carbonate by CO2? I mean does 19 ppm CO2 give you an extra 20 points worth of Calcium like I think I need?
Hi Savetheplants,

1.0 teaspoon of calcium carbonate (CaCo3) will increase the calcium (Ca) in 10 gallons of water by 12.7ppm it will also increase your carbonate hardness by about 1.0 dKH.

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post #8 of 43 (permalink) Old 06-28-2016, 05:35 PM
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I am working with CaNO3 in order to raise the Ca:Mg ratio closer to 4:1. Adding 1/4 tsp to 1 tsp of Dolomite by my calculations should be right. The CaNO3 is 15-5-0.
Since I use KCl for Potassium, intstead of KNO3, I'm not adding that much more nitrate to my tank. If I add the fully chelated iron @ 3-0-0 nitrogen, at the same time, am I still safe? Or is it too much nitrogen at once, and I should add the iron a week after adding the Dolomite and CaNO3?

I'm no chemist, and my calculations have killed fish before.
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post #9 of 43 (permalink) Old 06-28-2016, 06:22 PM
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I am working with CaNO3 in order to raise the Ca:Mg ratio closer to 4:1. Adding 1/4 tsp to 1 tsp of Dolomite by my calculations should be right. The CaNO3 is 15-5-0.
Since I use KCl for Potassium, intstead of KNO3, I'm not adding that much more nitrate to my tank. If I add the fully chelated iron @ 3-0-0 nitrogen, at the same time, am I still safe? Or is it too much nitrogen at once, and I should add the iron a week after adding the Dolomite and CaNO3?

I'm no chemist, and my calculations have killed fish before.
Hi @AWolf,

Regrettable your 1/4 teaspoon of CaNO3 to 1 teaspoon of dolomite (CaMg(CO3)2) is not yielding a 4:1 Ca:Mg ratio. It provides almost exactly a 2:1 ratio.

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post #10 of 43 (permalink) Old 06-28-2016, 08:00 PM
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Hi @AWolf,

Regrettable your 1/4 teaspoon of CaNO3 to 1 teaspoon of dolomite (CaMg(CO3)2) is not yielding a 4:1 Ca:Mg ratio. It provides almost exactly a 2:1 ratio.
Oh. I thought my dolomite was already 2:1, so by adding Ca I'd be bringing up the value.
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post #11 of 43 (permalink) Old 06-28-2016, 08:59 PM
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Oh. I thought my dolomite was already 2:1, so by adding Ca I'd be bringing up the value.
Hi AWolf,

I just double checked the numbers...still 2:1. Dolomite by itself is a little more than 1.5:1 (Ca:Mg).

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post #12 of 43 (permalink) Old 06-29-2016, 12:36 AM Thread Starter
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Quote:
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Hi Savetheplants,

1.0 teaspoon of calcium carbonate (CaCo3) will increase the calcium (Ca) in 10 gallons of water by 12.7ppm it will also increase your carbonate hardness by about 1.0 dKH.
I got some Calcium Carbonate from a brewer supply store. It would not dissolve in the tank. The pH in the aquarium is 7.0 which I think is too high to dissolve Calcium Carbonate. Maybe I'll try mixing some in a bucket of water with more CO2 and a water pump for a few days. Then I could add some epsom salt to raise my Mg up from 11 mg/l.
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post #13 of 43 (permalink) Old 06-29-2016, 01:08 AM
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Hi AWolf,

I just double checked the numbers...still 2:1. Dolomite by itself is a little more than 1.5:1 (Ca:Mg).
Thanks for that! So I will have to add 1.5 tsp CaNO3 to 1 tsp CaCO3 to get 4:1. Hummm....Nitrates getting up there now.
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post #14 of 43 (permalink) Old 06-29-2016, 02:48 AM
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Thanks for that! So I will have to add 1.5 tsp CaNO3 to 1 tsp CaCO3 to get 4:1. Hummm....Nitrates getting up there now.
Hi AWolf,

What size tank?

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post #15 of 43 (permalink) Old 06-29-2016, 03:03 AM
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I got some Calcium Carbonate from a brewer supply store. It would not dissolve in the tank. The pH in the aquarium is 7.0 which I think is too high to dissolve Calcium Carbonate. Maybe I'll try mixing some in a bucket of water with more CO2 and a water pump for a few days. Then I could add some epsom salt to raise my Mg up from 11 mg/l.
Hi Savetheplants,

Yes, calcium carbonate does not dissolve well in water. Try adding a teaspoon of apple cider vinegar (acetic acid) to the water and calcium carbonate mixture. The CaCO3 should dissolve, the reaction will give off a little CO2 gas.

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