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Before the importance of the buffer system can be understood it is essential to explain the definition and chemical basis of pH. The pH is the degree of acidity in the water. The acidity is determined by the proportion of hydrogen ions (H+) to hydroxyl ions (OH-) in the water. Extremely acid water (Ph 1.0) has very few hydroxyl ions, but many free hydrogen ions. Extremely alkaline water (pH 14) has very few free hydrogen ions but many hydroxyl ions. Neutral water (pH 7.0) has equal proportions of the two. Thus free hydrogen ions lower the pH, increasing the acidity of the water. Free hydrogen ions are released by the filter system as a by-product of the nitrogen cycle. Carbon dioxide released by living organisms in the water dissolves, making carbonic acid, which lowers the pH. There are also many organic acids in the detritus of a pond or aquarium, which lower the pH. The pH can rise due to removal of carbonic acid by plants and algae (which use carbon dioxide during photosynthesis). The pH of a pond or freshwater or marine aquarium is in a dynamic equilibrium. In other words there are many factors that exert an influence on the pH, and these are counteracted by the buffer system. The buffering capacity of a pond or aquarium can be defined.

As the ability of the water to resist changes in pH. The buffer system is comprised primarily of bicarbonates and carbonates, giving the buffer system the alternative name of Carbonate Hardness. However other bases such as hydroxides, silicates, phosphates, and borates contribute to the buffering capacity. Another name for the buffer system is the Total Alkalinity. All the above mentioned compounds are strong alkalis (they are termed bases - they have a high pH) So the total alkalinity is the sum of all these compounds.

How does the buffer prevent pH change?

Free Hydrogen ions are effectively 'mopped up' by the buffer, taking them out of solution, and preventing them from causing a decline in pH (a rise in the acidity of the water). Conversely when the pH begins to rise too high, due to a lack of free hydrogen ions the buffer system will 'release' some to bring the pH back down to the correct level.

How can I measure the strength of my buffer system?

Using the NT Labs KH test kit. This test kit adds measured drops of acid to a 5 ml sample of pond or aquarium water. Mixed in with the acid is an indicator chemical, which changes colour from blue to yellow at a precise pH. Thus the number of drops added to the sample needed to bring about the colour change is directly proportional to the strength of the buffer - or the ability of the water to resist a change in pH! Each drop is equivalent to 17.8 mg/L of Calcium carbonate - or put more conveniently one German degree of hardness (ºdH).

What is the ideal KH level?

Use the guide below to work out the ideal KH value for your fish:

Garden Pond
KH value (ºdH) should be Min 4 - Max 10

Koi Pond
KH value (ºdH) should be Min 4 - Max 10

Coldwater Aquarium
KH value (ºdH) should be Min 4 - Max 10

Tropical Community Aquarium
KH value (ºdH) should be Min 4 - Max 10

Marine Aquarium
KH value (ºdH) should be Min 8 - Max 14

Maintenance of KH in a marine aquarium is of absolute paramount importance, as the delicate marine life simply will not tolerate shifts in the pH of the water. Specialist aquaria such as soft water communities or discus tanks often have little or no KH value, as the pH is so low. Thus dramatic drops in pH are a constant risk, which must be prevented through regular water changes and scrupulous tank hygiene. Hard water communities often have high KH values and dramatic drops in pH only occur in poorly maintained systems. Soft water has very low carbonate hardness, and thus cannot resist strong changes in pH, If your tap water KH is below 4ºdH it will need a buffer replenisher. Use Koi Care KH up to raise the buffer of your water.

I live in a hard water area, how can I reduce the KH of my water?

Hard water has a higher KH due to the high amount of mainly carbonates dissolved in it. The KH can be reduced in one of two ways. Firstly a strong acid such as Koi Care pH down can be added to the water to use up some of the alkalinity, thus reducing the pH. Secondly the tap water could be run though a deioniser or reverse osmosis unit to completely remove all the minerals that affect the pH of the water. This deionised water can then be either used to dilute the tap water to the correct pH and KH. Alternatively the water can have the correct amount of minerals dissolved back into it to give the water the correct pH and KH.

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