Alkalinity Test Kit

Alkalinity Test Kits

Alkalinity is a measure of the buffering capacity of a water sample. A buffer reduces pH changes when an acid is added. If the alkalinity is high then the pH tends to be more stable. It is important then to consider both parameters. This test kit, by Salifert, is both simple to use, quick and accurate.

What is an alkalinity test kit

This is a simple test kit for analysing the alkalinity concentration in either fresh or salt water. It relies on adding drops of a chemical until a colour change occurs. This occurs at a precise point that indicates the alkalinity concenration in terms of mg/lire of calcium carbonate.

Why is alkalinity important?

Alkalinity is important because it has a profound influence on pH. This is a measure of the acidity of a solution and is important because this affects very many biological and chemical processes. If you’d like to find out more, here is an article on fish tank pH In summary, the important factors for an aquaponic system include;

  • pH determines the percentage of toxic ammonia present. A rise of just one point on the pH scale, e.g. pH 7.5 to pH 8.5, results in a tenfold increase in toxicity.
  • pH strongly influences the availability of plant nutrients. If the pH is outside the range 5.5 – 7.5 many nutrients will be ‘locked up’ and unavailable for plant growth.

Most aquaponic practitioners rely on tap water to operate their systems. This may well have a pH that is higher than desirable for an aquaponic system. The ability to reduce the pH will largely be determined by the alkalinity level. Unfortunately high pH tap water is strongly associated with high alkalinity levels. The ability to measure, and hence control, these two parameters is an essential skill for all operators of aquaponic systems.



How to use the Salifert alkalinity test kit

  1. Place a 4ml water sample in the test vial using the syringe provided.
  2. Add 4 drops of the indicator solution
  3. Carefully add, a drop at a time, the reagent. Gently swirl the vial after each addition.
  4. Continue adding drops until the colour changes from blue/green to orange/red/pink.
  5. The amount of reagent added can be read from the syringe.

Interpreting the results

The alkalinity level is read off the chart provided and gives an equivalent figure in terms of dKH. This is a measure of carbonate harness, also referred to alkalinity.

dKH can be converted into mg/litre of calcium carbonate, or meq/litre using the following conversion factors.

1 dKH = 17.9 mg/litre (or ppm) calcium carbonate (CaCO3)

1 dKH = 0.357 meg/litre


  • Always check the alkalinity of your water source when assessing it’s suitability for aquaponics. This applies to any fish or plant keeping scenario.
  • Record both pH and alkalinity levels regularly as they are strongly linked and have a tendency to decline over time.
  • A recommended optimum level in an aquaponic system would be in the range 50 – 150 mg/l CaCO3

You may also be interested in

Fish Tank pH

pH meters

Fish Ammonia – all you need to know



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