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pH and KH explained

If you are new to the hobby.

pH and KH explained

Postby Mick » Sun Mar 15, 2009 6:42 pm

The pH measurement of water is very simple to understand for experienced fish keepers but can be baffling to novices.The pH of water is determined by the ammount of free hydrogen ions in the water, the more free ions the more acidic the water. This is where the term pH was derived from (power of Hydrogen). Alkaline water will have a pH higher than 7.0, whereas acidic water will have a pH lower than 7.0
It is measured on a logarithmiic scale which means that the further the pH moves away from the neutral reading of 7.0 the greater the acidity or alkilinity increases per unit.
For example a pH of 6.0 is 10 times more acidic than 7.0 but a pH of 5.0 is actually 100 times more acidic than 7.0
Nitrates in the water can reduce the pH as they combine with the Hydrogen ions to form Nitric acid, another good reason for regular water changes. This is why the pH of tank water can drop just after a tank has cycled.

One of the most overlooked water parameters has to be the KH of the water, yet this is crucial to maintaining a stable pH in your tank.
KH (carbonate hardness) is the concentration of carbonate ions in the water. Carbonate ions will always try to attach to Hydrogen ions present in the water, the more that bond the higher the pH will be as the Hydrogen ions lose there power to acidify the water.
The by product of this process is carbonic acid whick breaks down into CO2 and disperses into the atmosphere. The KH of the water is the buffering capacity that it has with the pH
Using this knowledge any pH level can be created in the tank to suit your fish.
Sterile water from my RO unit has a KH of 0, the water from my HMA unit has a KH of 6. By mixing these two I can then raise or lower the pH to suit my needs.
The KH of the water should never be allowed to drop below 3 as this can cause a major pH crash.
KH should not be confused with GH (General Hardness)
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Re: pH and KH explained

Postby Graeme » Thu Jul 09, 2009 11:21 pm

Mick

Good article.

My pH was 7.8 last weekend prior to the 25% water change. With my new test kit I was able to measure KH. I dripped in 13 drops before the colour changed and according to the booklet, this gives me a KH of 130 mg/l. Your piece talks about much lower figures. Have I got a problem or am I doing it wrong?

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Re: pH and KH explained

Postby Mick » Thu Jul 09, 2009 11:27 pm

What you have to remember Graeme is that most of the tanks I have had required very soft, acidic water so my KH was often running at 4 with the pH often down to 6.0, this is why I added the warning about not letting the KH drop below 4, with your fish the water needs to be harder with an alkaline or neutral pH
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Re: pH and KH explained

Postby Anita » Thu Jul 09, 2009 11:41 pm

Good article Mick. I would agree it's most important to know what your readings are: especially if you live in a soft water area.
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Re: pH and KH explained

Postby Graeme » Thu Jul 09, 2009 11:44 pm

The pH has always been quite alkaline at 7.5 to 8.5. I understand the logarithmic mathematics shown from the number of free hydrogen ions in the water but a figure of 130 mg/l for the KH reading means nothing to me!
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Re: pH and KH explained

Postby Graeme » Tue Nov 24, 2009 12:30 am

Just found out that my KH of 130 needs to be divided by 17.9 to give a reading of 7.26 degrees of hardness. Is this the result I need to use when considering how hard or soft my water is? Or is this just a quirk of the API test kit?
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Re: pH and KH explained

Postby Mick » Tue Nov 24, 2009 8:26 am

It is a KH kit and not a GH kit?

My API kit just reads the number of drops. 4 drops in the tube gives a KH of 4 must admit I have never checked which scale this corresponds to :-):
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Re: pH and KH explained

Postby Anita » Tue Nov 24, 2009 10:47 am

API kH, drops are added until the water in the vile changes colour (forget now but is it yellow to blue or blue to yellow lol)
If the colour changes after 3 drops of test liquid you have a kH of 3, if it's after adding 7 drops then it's 7 etc...
My kit is oldish but I don't think they've changed the testing process.
Quite simple to use, although the colour changes are subtle, I have to put on my glasses and stand in font of the window where it's light lol.
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Re: pH and KH explained

Postby Graeme » Tue Nov 24, 2009 12:18 pm

My mistake, my old test kit was an API one, the new one is Nutrafin. For KH I add drops till the colour changes from blue to yellow. When that happens I multiply the number of drops by 10. This gives me my carbonate hardness in mg/L

I got the degrees of hardness thing from Wikipedia - Carbonate Hardness

And yeah, I have to put my glasses on too!!
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Re: pH and KH explained

Postby CEREDIGION123 » Sun May 27, 2012 11:37 pm

Mick wrote:The pH measurement of water is very simple to understand for experienced fish keepers but can be baffling to novices.The pH of water is determined by the ammount of free hydrogen ions in the water, the more free ions the more acidic the water. This is where the term pH was derived from (power of Hydrogen). Alkaline water will have a pH higher than 7.0, whereas acidic water will have a pH lower than 7.0
It is measured on a logarithmiic scale which means that the further the pH moves away from the neutral reading of 7.0 the greater the acidity or alkilinity increases per unit.
For example a pH of 6.0 is 10 times more acidic than 7.0 but a pH of 5.0 is actually 100 times more acidic than 7.0
Nitrates in the water can reduce the pH as they combine with the Hydrogen ions to form Nitric acid, another good reason for regular water changes. This is why the pH of tank water can drop just after a tank has cycled.

One of the most overlooked water parameters has to be the KH of the water, yet this is crucial to maintaining a stable pH in your tank.
KH (carbonate hardness) is the concentration of carbonate ions in the water. Carbonate ions will always try to attach to Hydrogen ions present in the water, the more that bond the higher the pH will be as the Hydrogen ions lose there power to acidify the water.
The by product of this process is carbonic acid whick breaks down into CO2 and disperses into the atmosphere. The KH of the water is the buffering capacity that it has with the pH
Using this knowledge any pH level can be created in the tank to suit your fish.
Sterile water from my RO unit has a KH of 0, the water from my HMA unit has a KH of 6. By mixing these two I can then raise or lower the pH to suit my needs.
The KH of the water should never be allowed to drop below 3 as this can cause a major pH crash.
KH should not be confused with GH (General Hardness)



Do they really still teach Hydrogen ions in school chemistry...BIG SIGH.......water dissociates to H3O+ and OH- :oops:
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