# This is probably general school boy knowledge...



## jimmy james (29 Sep 2011)

..but I'd be grateful if someone could help with the following.

When reading through the forum people refer to the GH/KH readings in single numbers, I'm looking to breed CRS and the suggested KH is 1-2 and GH 3-8. What I'd like to know is which calculation is generally used?

I have a Nutrafin KH/GH Test Kit and to test the GH I add 1 drop of reagent to 5ml tank water, the solution turns pink, then I continue to add them till it turns blue. Then I multiply the the total number of drops by 20 which then gives the General Hardness. For this example the total number of drops is 5 so the GH is 100. So far so good.

Then there is a conversion table on the back of the pamphlet where by you multiply the total by either 0.056 =dh°, or 0.07=Clark H°, or 0.1=fH°, or 1=hardness°, or 0.02=mEq/L. Now I assume its dh° so taken that the GH is 100 the dh° is 5.6. Do people then round up the number to 6? I'd also be interested in knowing what the other calculations are.  Thanks.


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## dw1305 (29 Sep 2011)

Hi all,
I don't think it is a "schoolboy question", in fact it is all a bit confusing. People generally use dGH/dKH German. The problem is that these are based on the conc. of CaCO3 (dKH) and CaO (dKH). Wikipedia is quite useful for the definitions:



> *Carbonate Hardness*
> _One German degree of carbonate hardness is equivalent to about 17.848 milligrams of calcium carbonate (CaCO3) per litre of water (17.848 ppm). Both measurements (mg/L or KH) are usually expressed "as CaCO3" – meaning the concentration of carbonate expressed as if calcium carbonate were the sole source of carbonate ions. Bicarbonate ions only contribute half as much carbonate hardness as carbonate ions, so bicarbonates that are present in the water are converted to an equivalent concentration of carbonates when determining KH.
> 
> *Example:*
> An aqueous solution containing 120 mg NaHCO3 (baking soda) per litre of water will contain 1.4285 mmol/L of bicarbonate, since the molar mass of baking soda is 84.007 g/mol. This is equivalent in carbonate hardness to a solution containing 0.71423 mmol/L of carbonate, or 71.485 mg/L of calcium carbonate (molar mass 100.09 g/mol). Since one degree KH = 17.848 mg/L CaCO3, this solution has a KH of 4.0052 degrees._





> _*dGH*_
> _General hardness is a measure of the concentration of metal divalent ions such as calcium and magnesium (Ca2+, Mg2+) per volume of water. Specifically, 1 dGH is defined as 10 milligrams (mg) of calcium oxide (CaO) per litre of water, which is equivalent to 0.17832 mmol per litre of elemental calcium and/or magnesium ions._


The conversion factors for degrees Clark etc  are here: <http://en.wikipedia.org/wiki/Water_hardness>

This is the tap water at my home:
Calcium (milligrams per litre) 119 (298 x 40% = 119)
Calcium carbonate (milligrams per litre) 298
Degrees German (ºdH) 16.7 (16.7 x 17.85 = 298)
Degrees French (ºf) 30
Degrees Clark 21
Sodium (milligrams per litre) 22
Conductivity 615 micro S(iemens)

cheers Darrel


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## jimmy james (29 Sep 2011)

Holy moly!  so for my test kit the dGH/dKH German is the x0.056 =dh°calculation? What did you use to test your parameters? Thanks.


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## dw1305 (29 Sep 2011)

Hi all,
I'm not familiar with the Nutrafin KH/GH Test Kit. I'll try and find out what it contains, because it goes from pink to blue it is an alkalinity test, it sounds like you add a known volume of an acid  and then neutralise it with alkali (like NaOH), and the pH reagent registers the colour change. It isn't quite a simple as that as you only have one reagent to add and this is simultaneously an alkali and an acid, so the it must be a buffer of some description.


> so for my test kit the dGH/dKH German is the x0.056 =dh°calculation?


 Sounds right, if degrees French is approx degrees German x 2 and you multiply by 0.1 (so approx x2 0.056) to convert to degrees French. 


> What did you use to test your parameters?


 I didn't, I got the values from Wessex Water. I've measured the conductivity a few times with a meter from the lab. which is how I know it is sometimes higher.

cheers Darrel


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