Tim's Tropical Fish - Saltwater

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pH - Saltwater Aquarium Water Quality

Water Quality

Water Type



< 7


> 7



pH is a scale that measures the "potential of hydrogen" - the number of hydrogen ions in water.  The scale ranges from 1 - 14.  The lower the number, the more acidic the water is.  The higher the number, the more alkaline the water is.  A value of 7 is neutral.  If the pH drops below 5, bacteria levels decrease to a point that wastes cannot be broken down and most fish will not survive.

Saltwater fish and invertebrates are sensitive to changes in pH, so it's important to ensure pH is stable. The acceptable range for pH is between 8.0 to 8.4 and  pH can be measured with a test kit or electronically.  The pH will tend to fall over time and will need adjustment.

The easiest way to raise the pH is through the addition of Kalkwasser or by ensuring high levels of calcium carbonate in the substrate by using natural reef sand and crushed coral.

Kalkwasser is a German word meaning "lime water" and it is basically calcium hydroxide. It is used to help maintain proper alkalinity by helping to restore proper pH levels as they naturally decrease in a tank over time. Kalkwasser also contains strontium and iodine, which replace trace elements which are absorbed by reef organisms. Kalkwasser does not contain nitrates or phosphates. It can be added whenever pure freshwater is added to top up an aquarium.  Its popularity has declined somewhat with the popularity of live rock, reef sand and coral substrates, as these also buffer the pH.

Water changes also help to stabilize pH.  Don't use the pH Up products sold for freshwater, as these contain phosphates that are harmful to saltwater fish and promote algae growth.