Understanding water pH

In its most basic terms, pH is the way of indicating whether an area of water is acid, alkaline or neutral.

pH is measured on a scale of 1 to 14: 1 is pure acid, 14 is pure alkaline and 7 is neutral.

Managing pH levels is vitally important to success in fishkeeping as fish must have a healthy and balanced environment to survive. A safe aquarium pH varies from fish to fish, but is typically between 6.5 to 8.5.

High or low pH can cause unexplained fish death, irritability in your fish, gasping at the surface and changes in colouration amongst other issues. 

Like many other water quality issues, changes in pH in your aquarium are invisible and unless you test your water regularly you will only notice the issue when things start to go wrong.

To better understand pH, we need to delve further into the chemistry of water. We all know that water’s chemical description is H2O. This is a mix of free positively charged hydrogen ions (H+) and negatively charged hydroxyl ions (OH-). It is the varying proportions of these ions that causes the differences in water pH. If there are more OH- ions then water will be more alkaline. But if there are more H+ ions then the water will be more acidic.

pH can be affected without you realising. All it takes is for new minerals to be added to the water. They will release ions which will contribute to the dominance of either the OH- or H+ ions in the water. These new minerals may be added to the water through rocks or wood used as décor, carbon dioxide from respiration or from decaying food or plants.

Did you know that for every increase of one pH, there is a 10-fold change in the concentration of hydrogen ions?

For instance, a pH of 6 is 10x more acidic than a pH of 7, and a pH of 5 is 100x more acidic than a pH of 7! As you’ll see, even a ‘small’ change in pH has a big impact on the water in which your fish live, so regular pH testing is crucial to happy and healthy fish.

pH lowering products often claim to contain a “buffer”. Simply put, a buffer is a way of using chemicals to prevent pH falling to a dangerous level. The chemicals will prevent the dominance of H+ ions and help a stable pH. Buffers can be added by the use of certain products, but they may be naturally present in tap water. Hard water contains minerals, and these minerals are the natural buffers that help stabilise the pH in your water. Soft water does not contain these mineral buffers, so if you live in a soft water area you may experience more issues with a fluctuating pH.

Fish have also learnt to adapt to changes in pH. Before you decide what fish you want in your aquarium it is worth considering the type of water you have and the natural pH.

Depending on their origins fish have become used to certain surroundings which generally include varying combinations of temperature, water hardness and pH. If you have naturally acidic, soft water you are going to have to work more to keep fish that prefer harder, more alkaline water so it is important to speak to your aquatic retailer before taking certain fish on.

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