pH Meter – the most important analytical device for aquaponics.

Top of your list of testing equipment, for any aquatic system, is a means of measuring pH. This is even more important for aquaponic systems. Drop Test kits and test papers are available but I thoroughly recommend investing in a reliable, and accurate pH meter. 

 What is a pH meter?

A pH meter is a device to measure the concentration of hydrogen ions and hence pH of a solution. It does this by measuring slight changes in electrochemical potential between two electrodes. One of the electrodes is made from special glass and the other is contained within the glass electrode itself. When placed in a solution there is an exchange of ions on the glass surface and this is measured and indicated by a digital readout. 

Three important things to note about pH meters include;

  1. The glass pH electrode is, unsurprisingly, delicate and care is needed to protect it from damage
  2. pH meters need frequent calibration against a solution, or solutions, of know pH in order to give accurate readings
  3. The electrode of all pH meters age and become less sensitive to the movement of ions. Although calibration will offset this there comes a time when the pH electrode will need to be replaced.

Why is pH important in aquaponics

I have covered this subject in much greater detail in my article on

. In summary, for an aquaponic system at least, the most important factors influenced by pH are;

1) Apera pH20 digital pH meter

Much much better than the cheap PH pens that you can get in different colours. Reading is quick and indicated by a smiley face. Comes with two buffer solutions (pre-made) and calibration in straight for


Additional items you may need

Although the pH electrode is able to be stored in the supplied pH 4.0 buffer it is recommended to use a dedicated solution of potassium chloride (KCl)


Sooner or later you will need replacement pH 4.0 and 7.0 buffers.

3 year shelf life. 250ml per bottle


  • all fish produce ammonia that is toxic to aquatic life if allowed to accumulate. This toxicity is profoundly affected by the pH because it is only the unionised form of ammonia (NH3) that is toxic. For every rise in one unit of the pH scale there is a tenfold increase in toxicity.
  • pH greatly affects the availability of most plant nutrients. Outside the range of 5.5 - 7.5 many nutrients become 'locked up' and not available for plant growth.

How to use the Apera pH meter

There are a great range of pH meters available for a great range of prices. I have been using this Apera for a while now and am very happy with it. It is a medium priced unit, as far as pH meters go, with an accuracy of 0.1pH. This should be sufficient for most peoples needs. The main thing to remember is that pH meters need to be quick to calibrate and give consistent and accurate readings. This particular model does not have a replaceable electrode but the cost of the whole unit represents excellent value for money and I prefer to replace the whole unit. If interested, Apera do supply a model,pH60, that does have a replaceable electrode and give a pH to two decimal points rather than one.

Testing procedure

  1. Remove storage cap. Rinse electrode in deionised water and gently dap excess water from the tip of the glass electrode using a tissue. Do not rub the delicate glass electrode.
  2. Place the electrode in the pH 7 buffer until a steady reading occurs. This is shown by a ‘smiley face’ and one of the reasons I like this meter is that this shows when a reading is stable. Calibration is achieved simply by pushing the CAL button.
  3. Two point calibration is recommended and is achieved simply by repeating the above using a different pH buffer, usually pH 4
  4. The meter automatically returns to recording mode following calibration

A few pointers to ensure maximum life and accuracy of pH meters

  • store pH electrode in solution of potassium chloride or pH buffer and do not allow to dry out. DO NOT STORE IN DEIONISED WATER.
  • Rinse electrode in deionised water and dap excess water between water sample.
  • Calibrate regularly to ensure accuracy. One a week would be about right for most users.

Interpretation of results from pH meters

For all pH meters results are quick and easy to record. They are compensated automatically for temperature. I find it best to plot them on a graph straight away as it helps to show up the overall trend. Most aquatic systems tend to drop fairly steadily in pH through the process of nitrification. However be aware that if the alkalinity is used up a rapid pH crash can occur that could threaten the life of the fish. For this reason it is a good idea to also record and plot the alkalinity levels on the same graph.

Alternative methods of recording pH

We all remember using litmus paper to record pH from our school days. This is very quick, easy and cheap and doesn’t involve any calibration like the pH meters. Unfortunately this is just not a very accurate method and not one I would recommend. The pH of a system plays a vital role in the lives of the fish and the plants and we owe it to them to know what it is at any one time. Unlike dissolved oxygen and ammonia it is not easy to tell the pH from fish behaviour. Plant deficiencies may give us a clue that something is wrong but for everyday management noting the pH should be considered essential.


  • Get yourself a reliable pH meter that will record pH values to 0.1.
  • Store the electrode in special storage solution (KCl) or pH 4 buffer. Do not store in deionised water. Even tap water would be better!
  • Calibrate your pH meter weekly, more often if you are getting inconsistent results.
  • Use a meter that also records water temperature and automatically adjusts the pH values
  • Treat the glass electrode with care and do not rub it wth tissue. A gentle dap should be all you need to remove excess water.
  • Replace the electrode and/or meter when the reading become unreliable. This can occur in a ‘year or two’.

You may also be interested in

The importance of pH

Alkalinity test kits

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