# KH and GH



## deezdrama (Jul 9, 2005)

ok my AP master kit came with a gh and kh test. Even after reading I dont fully understand what kh is and its importance. I know it means alkalinity and controls how stable your ph will be. But even after testing for it and knowing the results what can you do to make it better? What is better?


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## harrykaa (Jan 10, 2005)

deezdrama said:


> ok my AP master kit came with a gh and kh test. Even after reading I dont fully understand what kh is and its importance. I know it means alkalinity and controls how stable your ph will be. But even after testing for it and knowing the results what can you do to make it better? What is better?


Deezdrama,

What are your water parameters?

The GH (German Hardness or General Hardness) shows how much Magnesium (Mg) and Calcium (Ca) ions are dissolved into the water. Usually a good figure well tolerated by most fishes is between 3 and 10.

The KH (Carbonate Hardness) shows how much bicarbonates (HCO3) are dissolved into the water. As bicarbonates are the salt of acids, they also have inlfluence on water pH (not necessarily alkalinity) and the pH buffering capacity of the water. The rule is that the more bicarbonates you have in water, the higher is your KH and the higher is pH. Water having KH 6 or less is described as soft and KH over 6 is hard.
Piranhas (as tropical species) like soft water and slightly acidic water. So you could aim at pH 6,5-6.8 and KH 2-5.

Regards,


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## doctorvtec (May 15, 2004)

harrykaa said:


> The GH (German Hardness or General Hardness) shows how much Magnesium (Mg) and Calcium (Ca) ions are dissolved into the water. Usually a good figure well tolerated by most fishes is between 3 and 10.
> 
> The KH (Carbonate Hardness) shows how much bicarbonates (HCO3) are dissolved into the water. As bicarbonates are the salt of acids, they also have inlfluence on water pH (not necessarily alkalinity) and the pH buffering capacity of the water. The rule is that the more bicarbonates you have in water, the higher is your KH and the higher is pH. Water having KH 6 or less is described as soft and KH over 6 is hard.
> Piranhas (as tropical species) like soft water and slightly acidic water. So you could aim at pH 6,5-6.8 and KH 2-5.
> ...


In a nutshell...

GH will show your water hardness
KH will show your water buffering capacity (ability to hold pH)

A high KH level does not always indicate "hard water", nor does it "always" coincide with a high pH.


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## Dr. Giggles (Oct 18, 2003)

kH is your buffering capacity of your water while gH tells you if your water is soft or hard or anywhere in between.


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## deezdrama (Jul 9, 2005)

It says to add drops to the test tube till it turns the color but I cant tell if it turned the color or not


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## doctorvtec (May 15, 2004)

deezdrama said:


> It says to add drops to the test tube till it turns the color but I cant tell if it turned the color or not
> [snapback]1191668[/snapback]​


For KH the first drop should turn it blue. Add another drop and shake. Repeat until it turns from bright blue to yellow.

Its actually quite noticeable.


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## deezdrama (Jul 9, 2005)

mine never turned blue after the first drop


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## harrykaa (Jan 10, 2005)

doctorvtec said:


> In a nutshell...
> 
> GH will show your water hardness
> KH will show your water buffering capacity (ability to hold pH)
> ...


Doctorvtec,

Really in a nutshell,

KH (carbonate hardness) and GH (general hardness, German hardness) are really not so simple. Carbonate hardness (bicarbonates) is always in aquarium connected to calcium and magnesium and thus to GH. Actually one important component in GH is calsium carbonate, which has a major role in carbonate hardness. The other are magnesium sulphate, potassium sulphate and sodium chloride.
Perhaps I will write a short thread on carbon dioxide and bicarbonate chemistry.

A high KH means high concentration of bicarbonates which usually is the basic component in high GH (hard water). This is why water rich in bicarbonates (high KH) is commonly described as "hard".

Bicarbonates are dominant in slightly alkaline water. In strongly alkaline water carbonates dominate. And in acid water carbon dioxide prevails. Thus high KH and pH are connectec to each other. This (and the reactions with calcium, calcium carbonate and calcium bicarbonate) is what its buffering capacity is all about.

Regards,


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## Dr. Giggles (Oct 18, 2003)

Harry, it is possible though to have a lower pH with a high kH.


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## doctorvtec (May 15, 2004)

harrykaa said:


> doctorvtec said:
> 
> 
> > In a nutshell...
> ...


I will reiterate yet again. IT IS POSSIBLE to have a low pH with a higher KH reading.
_
"A high KH means high concentration of bicarbonates which usually is the basic component in high GH (hard water)" _

Note the word USUALLY. Just because you have a high KH, does not mean you will always have a high GH. Although many times GH, KH, and pH are linked, it is not a set in stone thing, and there are many occasions where the numbers do not coincide.

Not bashing you bud, just trying to explain to everyone that water chemistry is not always set in stone.


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## Brett (Sep 28, 2004)

doctorvtec said:


> harrykaa said:
> 
> 
> > doctorvtec said:
> ...


Please tell me how to achieve this condition of low PH with moderate/high KH. I use 100% RODI water and rebuild it with Kent R/O Right and baking soda and still cant get a low PH with a KH of 3 or higher. PLEASE enlighten me, I have been working on figuring this out for at least a year!!!!! The best I can do is 3 DGH, 3 DKH, and a PH of 7.5, I want a DGH and DKH of 3 but a PH of 7.0ish range.


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## doctorvtec (May 15, 2004)

It depends what you consider low pH.

I have a pH of 7.2 and a DKH of 8.

I consider this a low pH with a high DKH.


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## harrykaa (Jan 10, 2005)

doctorvtec said:


> It depends what you consider low pH.
> 
> I have a pH of 7.2 and a DKH of 8.
> 
> I consider this a low pH with a high DKH.


Doctorvtec,

OK, you are right in saying that you can have a high dKH with a low pH, if you consider dKH 8 high and pH 7.2 low.

In my reply I forgot to say I meant a high dKH if it is over 10 and a low pH if it is less than 6.5.

But then again, its OK you have corrected my reply.

Regards,


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## Brett (Sep 28, 2004)

doctorvtec said:


> It depends what you consider low pH.
> 
> I have a pH of 7.2 and a DKH of 8.
> 
> ...


I would do cartwheels if I could get my water to the ph and kh yours is!! My water comes right out of the RO/DI at 6.4ph, when I add a bare minimum of RO Right to remineralize the ph goes to 6.8 but the DKH still reads around 0-1 so I add straight baking soda to boost the alkalinity to 3 DKH and the ph jumps to 7.5. How do I do this different?? I don't want a KH less than 3 or I'm afraid my ph will crash.


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