The Weald Aquatics Blog - pH in the aquarium - another blog post from Weald Aquatics | Aquarium & Pond Fish Shop in Kent


Coolings Green & Pleasant
Main Road, Knockholt, Kent TN14 7LJ

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pH in the aquarium

Blog post written by Gary | 21 October 2016 | Category: Aquarium maintenance

The pH value of water in simple terms indicates whether water is acidic, alkali or neutral.

The pH scale starts from 0 which is the most acidic going up to 14 being the most alkali. A pH of 7 is neither acidic nor alkali and is considered neutral. The pH scale is logarithmic which means a small change in the pH value  actually equates to a large change to the water as each pH unit is a tenfold increase or decrease on the previous value.

Fish have evolved to live in water as low as pH5 to as high as pH9.5. However most freshwater fish live between pH6 and pH8.2. When keeping a mixed community of freshwater fish a pH of 7 to 7.2 is ideal. Both African Cichlids and marine fish have specific pH values for their aquarium setups.

Excessive high or low pH levels and fluctuations will cause stress in the aquarium, possibly leading to poor fish colour, poor appetite and a lowering of the resistance to disease. To keep the aquarium water at ideal pH levels, regular testing of the aquarium water is essential. It will indicate if the pH is gradually being lowered by the action of the fish waste being broken down into nitrates and carbon dioxide produced by the fish. Regular water changes will usually bring the aquarium water back to a pH of 7 to 7.2 (depending on the pH of the mains water).

To keep aquarium water at a specific pH value there are buffers available, which, as the name suggests, will keep the water at the specified pH level. Also available are additives which will raise the hardness of soft or RO water whilst keeping the pH at about pH7. 


Products for adjusting the pH of aquarium water
Products for adjusting the pH of aquarium water