Ph, Kh, Gh

Water Chemistry: pH, GH and KH What are they all? – Scott Thomson

Per Hydrogen (pH)

The pH of the water is a measure of the balance between the Hydrogen (H+) and Hydroxide (OH) ions in the water. I think most of us know that low pH is acidic and high pH is alkaline or basic. Hence a pH of 5 is slightly acidic water, a pH of 7 is neutral and a pH of 8 is alkaline water.

The pH scale is a logarithmic scale. In other words a pH of 6.0 is 10 times more acidic than a pH of 7.0 and a pH of 5.0 is 100 times more acidic than a pH of 7.0. As a keeper you need to be aware that it is not a difference of 1 when you go from 6.0 to 7.0.

Ways to lower pH
Filtering water over peat
Add bogwood to the tank
Inject carbon dioxide CO2
Use a commercial acid buffer
Water changes with softened water or RO (Reverse Osmosis) water

Ways to raise the pH
Aerate the water, driving off the carbon dioxide (CO2)
Filter over coral or limestone
Add rocks containing limestone to the tank or use a coral sand substrate
Use a commercial alkaline buffer

Carbonate Hardness (KH)

This is an area where many people get confused. One of the reasons the term alkaline is avoided a bit and the term Basic is used for the pH scale is because this reading is measuring the alkalinity of the water. It is not the same as alkaline.

The alkalinity is a measurement of the waters buffering ability, or its ability to absorb and neutralise acid. Clearly the more alkalinity or the higher the Carbonate Hardness of the water the less likely you will incur pH swings in the water. It is therefore important to get this figure reasonably high to stabilise the water.

Exactly how high you want your dKH (degrees of KH) will depend on what pH you choose to use. To people keeping fish from the African Lakes this is the life and death of their fish. Those fish live in very stable high pH conditions, they do not like change and the conditions can be difficult to imitate. Fortunately turtles are not quite so sensitive. However, I do think that basic fish keeping can teach the aquatic turtle keeper a thing or two about water.

Ways to increase kH
Adding sodium bicarbonate (baking soda). One teaspoon of baking soda added to 50 liters of water can raise the kH of the water by approx 4 deg dH without a major affect on pH.
Adding an air stone to increase surface turbulence driving off carbon dioxide (CO2)
Adding commercially available products to increase buffering capacity

Ways to lower kH
Injecting carbon dioxide (CO2)
Use reverse osmosis (RO) water. You can mix tap water with reverse osmosis water to achieve the desired kH.
Adding commercially available products to decrease the buffering capacity.

Do not use distilled water as it has no dissolved salts and hence no buffering ability. Add a small amount of acid (eg uric acid) and it will shift the pH very rapidly. It is also highly osmotic and will react with the turtles renal system.


General Hardness (GH)

This is essentially a measurement of Magnesium and Calcium ions in the water. Again it is measured in the German degrees of hardness scale or parts per million. This is what is generally meant by soft and hard water which are terms people should be familiar with. The table below shows comparisons between parts per million, the dH scale and the generalised concepts of soft and hard water.

Ways to increase gH
Adding limestone to the aquarium (this will also increase kH which in turn will increase pH)
Adding calcium carbonate will raise gH and kH

Ways to reduce gH
Adding peat moss to your filter
Use commercially available water softening pillows or a water softener (this removes calcium and magnesium ions and replaces them with sodium ions. Many people feels that this is an unacceptable method of softening water as many fish that prefer soft water don’t like sodium either.
Mixing tap water with reverse osmosis (RO) water.

General Hardness Table

0 to 4 dH       0 to 70 ppm         Very Soft
4 to 8 dH       70 to 140 ppm     Soft
8 to 12 dH     140 to 210 ppm    Medium Hard
12 to 18 dH   210 to 320 ppm    Fairly Hard
18 to 30 dH   320 to 530 ppm    Hard

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