# Dosing Calcium Carbonate to Raise KH



## AaronT (Apr 26, 2004)

I'm putting together a 5.5 gallon tonina tank. I normally use my tap water, which is 6.8 pH, 12 GH, and 3 KH. I want to cut my tap water with distilled water and raise the KH back up to stable using calcium carbonate. How much calcium carbonate dosing will raise 1 gallon of water 1 degree KH?


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## John S (Jan 18, 2005)

instead of calcium carbonate just use baking soda that way your GH will not go up


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## AaronT (Apr 26, 2004)

I know baking soda works too, but baking soda increases the conductivity of the water, which if I'm not mistaken is not a good thing. GH does not go up as much with calcium carbonate as it does with calcium chloride. I want to use the calcium carbonate to make sure calcium levels are sufficient.


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## John S (Jan 18, 2005)

good point didnt think of that one ](*,)


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## cS (Jan 27, 2004)

I am of the opinion that the minor increase in conductivity resulting from the mere rise of 1 dKH via baking soda is negligible. Nonetheless, to raise 1 US gallon by 1 dKH, you'd need 0.0757 gram CaCO3 (~1/32 teaspoon). That would also increase GH by 1 degree (Ca content only).

Please check my math: 2 teaspoons CaCO3 (~4 gram) per 50 liter will raise GH and KH by 4 degrees.


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## david lim (Mar 30, 2004)

grandmasterofpool said:


> I know baking soda works too, but baking soda increases the conductivity of the water, which if I'm not mistaken is not a good thing. GH does not go up as much with calcium carbonate as it does with calcium chloride. I want to use the calcium carbonate to make sure calcium levels are sufficient.


Anything that dissolves into ions adds to the conductivity of a solution, or are my memories of undergrad general chemistry deceiving me? For instance CaCo3 would be Ca(2+) and CO3(2-).

Definition: Conductivity is a measure of the ability of a material to conduct electric current.
(from here: http://www.ktf-split.hr/glossary/en_o.php?def=conductivity)

GH and KH both add to the total conductivity of your solution. Softwater fish enjoy low conductivities for breeding but for daily life I've found it to be unneccessary. In fact, I have successfully bred wild A. bitaeniatia in a KH7, GH8 heavily planted tank (but this isn't always true). For the most part, as long as the plants are healthy then the fish will be healthy.


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## titan97 (Feb 14, 2005)

I was thinking the same thing David. And Calcium chloride should add more conductivity that calcium carbonate. CaCl2 would provide 3 free ions (one Ca++ and two Cl-). Baking soda would do the same as the CaCl2, since NaHCO3 has 3 ions as well. But then again, CO3-- is in equilibrium with HCO3- and H2CO3, therefore making less of it available in purely CO3-- form. 
But what does conductivity have to do with anything in the aquarium?


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## cousinkenni (Jan 24, 2005)

*About dosing CaCO3*

How are you guys measuring this stuff?

Chemistry:

CaCO3 100g/mol
CO3: 60g/mol
Ratio 0.60g/mol CO3 in CaCO3

0.60 * 4g = 2.4gCO3
2.4g = 2400mgCO3
2400mg in 50L = 48mg/L or 48ppm
48ppm/17.86ppm/1dH = 2.7 dKH

To work backwards:

1gal = 3.8L
XmgCO3/3.8L = 17.86ppm(1dKH)
X = 67.86mg
67.86mg = .06786g
.06786gCO3 / .60 = .113gCaCO3 needed

So here is some measeurements that I took on an analytical balance last night:

(keep in mind measurement error)
1st time weighing: 1/8tsp weighs 0.4608
2nd time weighing: 1/8tsp weighs 0..6825

Average weight for 1/8 tsp = 0.572g

0.113/.572 = .2
so roughly 1/4tsp in 10gal raises it 1dKH

Correct?

Any objections? Please someone tell me I am calculating this stuff wrong......Am I not understanding some basic principal?

Ken T.


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## david lim (Mar 30, 2004)

Your calculations look good, Ken.



titan97 said:


> I was thinking the same thing David. And Calcium chloride should add more conductivity that calcium carbonate. CaCl2 would provide 3 free ions (one Ca++ and two Cl-). Baking soda would do the same as the CaCl2, since NaHCO3 has 3 ions as well. But then again, CO3-- is in equilibrium with HCO3- and H2CO3, therefore making less of it available in purely CO3-- form.
> But what does conductivity have to do with anything in the aquarium?


Conductivity is usually what scientists measure in the field to understand the hardness of a solution. Measuring conductivity will measure everything that is able to promote electrical currents in solution.

I don't believe fish are able to discern Ca, C03, Fe, etc in the water column, but they can sense the conductivity.

Many breeders attain breeding conditions by droppin the conductivity of their tanks (ie GH and KH). In areas like the rainforests of S. America, fish sense the seasons through many factors including conductivity. Basically, a drop in conductivity tells a fish that there is more "pure" water (rain water which lacks ions) entering the river systems and this might coincide with the wet season (ie. good time to get it on). Fish also sense changes in diurnal cycles, pH, water depth, relative temperature changes, etc. for the right breeding conditions.

Sorry, I didn't mean to jack the thread.


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## titan97 (Feb 14, 2005)

Thanks for the conductivity info. I'm a Biochemist by education, but that doesn't mean I already know everything about biochem. I enjoy everything I've learned here at APC. Keep up the good info.

-Dustin


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## AaronT (Apr 26, 2004)

Thanks for the responses. I don't have a good gram scale yet so I may just go w/ pure distilled water and cheat using Sea Chem's equilibrium.

Interesting discussion guys.


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## cS (Jan 27, 2004)

cousinkenni said:


> Any objections? Please someone tell me I am calculating this stuff wrong......Am I not understanding some basic principal?


Your math is flawless but it reflects CO3-- instead of HCO3--, which is what it actually exist as in our tanks. ;-)

*CaCO3 + H2O + CO2 => Ca++ + 2(HCO3-)*

So, for every mole of CO3-- added, we get 2 mole of HCO3-. Please pardon my stoichiometry:

CaCO3: 100 g/mol
HCO3: 61 g/mol
1dKH = 21.8 ppm HCO3










4880 mg HCO3 / 50 liter = 97.6 ppm HCO3

97.6 ppm HCO3 * (1 dKH / 21.8 ppm HCO3) = *4.47 dKH*

So, 4 grams of CaCO3 in 50 liter of water will raise the KH by approximately 4.47 degree.

---

I didn't actually measure 2 teaspoon CaCO3 to be 4 gram. It was pasted into my file from somewhere a long time ago. I don't remember where; so I can't verify. Apologies. [smilie=d:


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## cousinkenni (Jan 24, 2005)

Hey CS,

One question for you.......

Why do you divide by 21.8 instead of what Edward says to divide by which is 17.86. There is quite a difference between the two numbers. So what number is correct and why would Edward post the incorrect number if your number is correct?

Thanks for the reply. I don't know why I didn't think of it before.
Stupid, stupid kenni ](*,) 

Ken T.


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## cousinkenni (Jan 24, 2005)

Hey Cs,

I just thought of another question for you.........

What about NaHCO3

From my calculations (once again I weighed 1/8tsp) 0.5217g NaHCO3 should give 4.78ppm rise in 78L. Is this the same number that you get or does NaHCO3 dissociate to form another ion inconjunction with CO2?

Another way of thinking about it is that 4g NAHCO3 would give a 2.66dKH rise in 50L Correct?

Thanks,

Ken T.


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## cS (Jan 27, 2004)

cousinkenni said:


> Why do you divide by 21.8 instead of what Edward says to divide by which is 17.86. There is quite a difference between the two numbers. So what number is correct and why would Edward post the incorrect number if your number is correct?


Which is heavier: one ton of bird feathers or one ton of steel? To put it another way, which is longer: 1 meter or 100 centimeter? They all express the same quantity right? :mrgreen: ...except that each is measured in different units. The same concept applies here:

1dKH = 17.86 ppm CaCO3
1dKH = 21.8 ppm HCO3

KH (and GH) is usually expressed as CaCO3 equivalents so that's why a lot of people omit the CaCO3, assuming that it is understood/implied. You used CO3 so 17.86 is the appropriate conversion factor, whereas I used HCO3 so 21.8 is my conversion factor. They're all the same thing.



cousinkenni said:


> From my calculations (once again I weighed 1/8tsp) 0.5217g NaHCO3 should give 4.78ppm rise in 78L. Is this the same number that you get or does NaHCO3 dissociate to form another ion inconjunction with CO2? [...] Another way of thinking about it is that 4g NAHCO3 would give a 2.66dKH rise in 50L Correct?


That is absolutely correct Ken. [smilie=k:

Techinically: yes, the HCO3-- does go on to react with CO2 but that's a different calculation: one that leads us to the pH/KH/CO2 relationship that everyone uses to measure CO2 concentration. ;-) But for our purpose of calculating KH, no, that's not important because NaHCO3 is VERY soluble in water, forming Na+ and HCO3- (which is stable at our pH) directly. This is why everyone in this thread advises grandmasterofpool to use baking soda instead of CaCO3.

[b]NaHCO3 => Na+ + HCO3-[/b]

Conversely, CaCO3 is not very soluble in water. It needs an acid to do so. In our tanks, that acid is the carbonic acid (H2CO3), formed from the injection of CO2 gas. That is why it is included in the equation below and not the NaHCO3 equation above.

*CaCO3 + H2CO3 => Ca(HCO3)2 => Ca++ + 2(HCO3--)*

*CO2 + H2O <=> H2CO3 <=> HCO3- + H+* _(I skipped this part in my previous post and just shorthanded the whole thing. Sorry. But this is the source of the carbonic acid that is required to dissolve CaCO3.)_

***Recall the solubility rules from general chemistry (I don't recall but I've just googled the net) that (1) compounds of CO3-- are not soluble in water except those with NH4+ and Group IA; but (2) compounds of HCO3- with Groups IA & IIA metals are. So, looking back, we see that Ca*CO3* is not soluble until it becomes Ca(*HCO3*)2 whereas Na*HCO3* is immediately soluble. If my teacher had an aquarium in class, then I would have paid more attention. Live and learn. [smilie=l:

---

Could you have asked a more involved question? Speaking fo which, please don't ask me where babies come from. ::laughs::


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## cousinkenni (Jan 24, 2005)

CS,

Thanks for the involved answers, I appreciate them greatly. I would much rather have an involved answer than a two word answer. I can't believe I forgot about the dissociation of CaCO3. I should have remembered that from basic limnology years back. You have to forgive me, I changed profession from marine/freshwater biology to cancer research about six years ago and only limited knowledge remains. Too bad I cannot find my limnology texts anymore .

Ken T.


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## discus (Jul 20, 2004)

I think i need to get my chem books out again.
Great stuff guys

Discus


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## cousinkenni (Jan 24, 2005)

Hey Cs,

Just to stir my memory again............

It is the KH, CO2, pH relationship right? So the Charts that Edward posted shows how much CO2 will be dissolved in H2O at a certain pH and KH correct?

I asked this question to Edward a while back and while he did answer my exact qustion he didn't go into detail about the equation like you have.

From what I remember from my texts from way back when, can't this relationship (CO2 + H2O <=> H2CO3 <=> HCO3- + H+) be looked at in another light?

This relationship that you posted is an equilibrium equation. So in essence you could still obtain a 30ppm co2 and have a very very low KH right? All we have to do is inject (or add more) CO2. The only problem with this is that the pH will take a drastic dive from all the excess H+ ion floating around.

The reaon I ask all this is because when you are taught this (from texts), the dependant factor is usually the pH, not the CO2 as shown in the table. Since we as aquarium keepers only "live" within a reasonable pH (6.0 - 8.5) we make it seem as though CO2 is the dependant factor.

So for us, by adding more HCO3- (in the form of CO3-- from CaCO3) we are just shifting the equilibrium to the left of the equation which also removes some of the H+ thus keeping the pH in check, right?

Does my question/statment make any sense?

I guess I am referring to the Diel pH fluctuations which would normally occur in soft, freshwater lakes especially during the summer or if Eutricication occurs.

Thanks,

Ken T.

Sorry about the even more involved question maybe next time I will ask where babies come from (it might be easier to answer)


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## Edward (May 25, 2004)

cousinkenni said:


> The reaon I ask all this is because when you are taught this (from texts), the dependant factor is usually the pH, not the CO2 as shown in the table. Since we as aquarium keepers only "live" within a reasonable pH (6.0 - 8.5) we make it seem as though CO2 is the dependant factor.


Hi
There is no need to be alarmed by low pH. Most plants and fish will be fine. I run few tanks with KH of zero and 0.25 degree. The pH get as low as 4 and 5. The plants and Tetras love it.

Edward


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## drbdc (Mar 30, 2005)

Why are you running no Kh? pH of 4! That's stomach acid levels! I can digest my fish dinner at that pH! ) I hope you don't have snails! I would think that the CO2 is too high because on a reef tank that is the pH coming out of a calcium reactor which is done with CO2 as well. It causes all Ca to dissolve which would include any invert shells/skeletons. I'm not that experienced with plants yet but if any Ca is used by plants, it will leach it out and I know I add it to the ro/di water for some reason.


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## GillMan (Feb 22, 2005)

OK, now for something completely different...So I've done a CaC03 test (La Motte) and got 54 ppm, and I've done a Ca++ test (Nutrafin) and got 40 ppm. My GH is 5.5. So, knowing both types of calcium present and the GH, what is the formula for calculating the amount of magnesium present in the GH test?

Thanks in advance.


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## Edward (May 25, 2004)

Hi GillMan
The formula for Mg can be found in FAQ here on Fertilizing forum.

Edward


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## Edward (May 25, 2004)

drbdc said:


> Why are you running no Kh?


 Neither the plants nor acid loving tetras require it of which many breed at pH levels of only 5 and lower



> I hope you don't have snails!


 Sure I do and they look happy.



> I would think that the CO2 is too high because on a reef tank that is the pH coming out of a calcium reactor which is done with CO2 as well. It causes all Ca to dissolve which would include any invert shells/skeletons. I'm not that experienced with plants yet but if any Ca is used by plants, it will leach it out and I know I add it to the ro/di water for some reason.


 I keep Ca at 20 - 30 ppm.

Edward


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