# 4 deg kH water



## ray-the-pilot (May 14, 2008)

OK I'll probably draw a lot of crickets on this one but who knows?

What is the molarity of 4 deg kH water. I calculated that it is 0.0142 molar. 

That means that 0.0142 molar NaOH, NaHCO3, 1/2 Na2CO3, KOH, 1/2Ca(OH)2 etc. will all be 4 deg kH water. ie. anything that supplies an alkalinity of 0.0142 molar in the form of OH, HCO3 or CO3 will be 4 deg kH water.

Can anyone verify this?


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## ray-the-pilot (May 14, 2008)

Any suggestions as to where to post this and get a response.
I guess APC kicked off everyone with a brain.


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## HeyPK (Jan 23, 2004)

Yup, we kicked 'em all off. Try the Planted Tank Forum.


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## Left C (Jun 14, 2005)

I know that the pH/KH/CO2 relationship only works with carbonates. Some of your compounds do not contain carbonates (CO3 --).


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## ray-the-pilot (May 14, 2008)

Left C said:


> I know that the pH/KH/CO2 relationship only works with carbonates. Some of your compounds do not contain carbonates (CO3 --).


The carbonate buffer system includes [OH] and [H]

On a molar basis NaHCO3 has more CO2 than Na2CO3 and [OH] has none. This is only the initial state. When dissolved in water, and placed in a drop checker, they all start absorbing CO2.

The NaOH reacts like this:

OH- + CO2 -> HCO3-

Eventually all of them will absorb CO2 until they reach equilibrium with the atmosphere. The final concentration of CO2 dissolved depends only on the initial amount of Na+

I've been using NaOH in my dropchecker for some time and it works well. It is much easier to calibrate than NaHCO3


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## Left C (Jun 14, 2005)

Check this out, Ray.

I used duchy's formula (below) for making a 4 dKH solution to calculate the molarity. My molarity calculation is 10 times smaller than yours or off by one decimal place. You got 0.0142 and my result is 0.00143. (I'm not concered by the one integer difference {142 vs 143}. This could be due to rounding.)

"Add 6 grams of bicarbonate of soda to one liter of distilled water. This gives you one liter of water with a KH of 200 dKH. Now take 10 ml of that water and mix with 490 ml of distilled water (a dilution of 1 in 50) and you get 500 ml of 4 dKH water.

regards,
dutchy"

So, 6g of NaHCO3 added to 1L = 200 dKH
Divide by 50, 6g NaHCO3 added to 1L ÷ 50 = 200 dKH ÷ 50
0.12g NaHCO3 added to 1L = 4 dKH
Molarity (M) of NaHCO3 = 84 g/mole
M of 4 dKH solution = 0.12g NaHCO3 ÷ 84 g/mole = 0.001429 = 0.00143
M = 0.00143

*** Also, I see that you took into account the Normality (N) for your solutions as well as the Molarity (M) because valences are involved. Some of the solutions have more than one positive ion.
Reference: "Molarity, Molality and Normality" by Roberta C. Barbalace: http://environmentalchemistry.com/yogi/chemistry/MolarityMolalityNormality.html

Take care,
Left C


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## ray-the-pilot (May 14, 2008)

Left C said:


> http://www.youtube.com/watch?v=J834KH43YgE&feature=related
> 
> Check this out, Ray.
> 
> ...


Hey thanks. I was already aware of the 10x factor. I made a typing error in my post. But you are right we are looking for a 0.0014 normal solution!
(maybe it is a .00142 molar kH solution).
Here is the way I calculated it:

17.8 mg (CaCO3/L/deg kH) x 4 (deg kH) x 1 (g) /1000 (mg) /100.089 (g/mole CaCO3) x 2 (mole kH) / 1 (mole CaCO3) = 0.00142 (mole kH/L) = 1.42 mM kH


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## Left C (Jun 14, 2005)

Be careful with your sodium hydroxide. I had a bad experience with it one time. ... It can be wicked stuff!

I believe that I will stick with baking soda for my 4 dKH solutions.


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## Se7eN (Sep 23, 2010)

Baking soda is easier and safer in my opinion.


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## Left C (Jun 14, 2005)

The hygroscopic nature of baking soda can make it a bit tricky to weight out. Then trying to dry it in an oven causes another set of problems. I use one of the dilution formulations to make it. I start with a fresh box of baking soda. I check my results with my LaMotte Alkalinity test kit and tweak as needed. This is fine for my use. This is really just a close approximation of the CO2 level and not a precise measurement. Using this and watching our fauna allows fine tuning to some extent.


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## ray-the-pilot (May 14, 2008)

Left C said:


> The hygroscopic nature of baking soda can make it a bit tricky to weight out. Then trying to dry it in an oven causes another set of problems. I use one of the dilution formulations to make it. I start with a fresh box of baking soda. I check my results with my LaMotte Alkalinity test kit and tweak as needed. This is fine for my use. This is really just a close approximation of the CO2 level and not a precise measurement. Using this and watching our fauna allows fine tuning to some extent.


Since I am a chemist by profession I am a little anal about stuff like this. I have calibrated NaOH and HCl solutions that are standardized against CaCO3 and KHPh reference standards. When I say 4 deg. kH I mean 4.00 +/-.05.

My original intent of this post was to have someone check my calculations.


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## Left C (Jun 14, 2005)

ray-the-pilot said:


> Since I am a chemist by profession I am a little anal about stuff like this. I have calibrated NaOH and HCl solutions that are standardized against CaCO3 and KHPh reference standards. When I say 4 deg. kH I mean 4.00 +/-.05.
> 
> My original intent of this post was to have someone check my calculations.


Then we have your answer then. When checking your calculations, we found that your calculation was off by 1 decimal place and that could of easily been a typo.

The conversion that I use for converting ppm of CaCO3 to either dKH or dGH in German degrees is 17.86 which rounds up to 17.9. But, I've also seen people use 17.8 for the conversion as you used.
references: 
http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html
http://aquaticconcepts.thekrib.com/Articles/Water_Chemistry.htm
http://www.lamotte.com/pages/common/techtips/convert.html
http://www.saltyzoo.com/SaltyCalcs/AlkConv.php

But, even if we make a solution with a 4.00000 ... dKH and add it to our drop checkers with the bromothymol blue pH indicator solution, we still can't very accurately measure our CO2 level. We can only estimate it with these tools. But, these tools are better for approximating the CO2 level than what we had before the 4 dKH carbonate based solutions came about a few years ago. The other alternatives we had were using expensive lab equipment or using aquarium water in our drop checker solutions. Maybe someone can come up with an inexpensive spectrophotometer type of device to read the color better than our eyes and then report the CO2 level.

Good luck with your projects!


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## Se7eN (Sep 23, 2010)

I make 4dkh all the time. I normally make it in 5 or 10 gallons at a time to make sure its where I want it, as close to 4dkh as possible. I normally sell off what I have extra, or pour it out....

I have no experience with the molar but am interested to learn more about it. I like to read the forums on a daily basis but have not read much about it except on here...


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## Left C (Jun 14, 2005)

Hi Se7en

Are you saying that you want to be able to calculate molarity and normality? This little link below tells you about what it represents and how to calculate it starting with Avogadro's number. I found plenty of examples showing how to calculate molarity and normality, but you need to know what a mole of a substance is, how many atoms are in a mole, use the periodic table and so on. Here's a decent link about it: http://environmentalchemistry.com/yogi/chemistry/MolarityMolalityNormality.html


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