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Starting an aquaponic system

This experiment is an introduction into the functions and management of a small aquaponic system. Like a home aquarium, an aquaponic system requires special attention in the first weeks, since the microbial community in the water and in the plant boxes need some time to get established.

Learning goals

Background information

There are at least three species of living organisms in an aquaponic system. There are fish, plants and bacteria. In our small classroom system we will have about four goldfish in the aquarium, 60 plants in the plant beds and about 100'000 billion of bacteria and other very small species in the gravel or LECA. Bacteria have been on this planet for 3 billion years while man exists for at most 3 million years, and our civilisation for just 10'000 years. A human being couldn't survive a day without the help of bacteria and neither would the fish and plants in our classroom system.

The fish need oxygen to survive - in the same way as human beings, i.e. by breathing - but the fish take oxygen from the water and excrete ammonium and carbon dioxide over the gills. There is also ammonium in the excrements (faeces) from the fish. The ammonium in the water can become dangerous to the fish. The bacteria can transform ammonium into a substance (nitrate) which is harmless to the fish and at the same time an important plant nutrient. This process is called nitrification and it is necessary to supply the plants with nitrogen fertilizer.

So the first thing we need to do before we put any fish in the aquarium, is to start growing a lot of bacteria in the plant boxes, so that they can take care of the fish excrements i.e. the ammonium in the water.

Another important factor influencing the water quality is pH. It indicates whether the water is acidic, neutral or basic. The pH is measured on a scale of 1-14 with 7 being neutral. Is the pH lower than 7, the water is acidic, if it is higher, the water is basic. Depending on the fish species, the optimum pH varies. Goldfish tolerate variations in pH much more than other fish species, but to avoid stress, the pH should stay within the range of 6.5 - 8.

Time requirement

The starting phase should last at least for three weeks.

Material requirement

Aquarium test kit for nitrite and nitrate
  • 1 classroom aquaponic system (see experiment 1 in this teaching unit)
  • 1 aquarium test kit for ammonium (NH4+)
  • 1 aquarium test kit for nitrite (NO2-)
  • 1 aquarium test kit for nitrate (NO3-)
  • 1 aquarium test kit for pH
  • 1 bacteria starter package for aquarium filters
  • 1 aquarium thermometer

Let's start

See and feel

Didactical comments

In order to understand the process of nitrification, or what happens in the filter, some basic knowledge in chemistry is required. However it is possible to explain it in using metaphors: two little animals (bacteria) are responsible to transform the poison (ammonium) into a non toxic substance (nitrate), which at the same time will feed the plants. With the ammonia and nitrite test kit we indirectly measure the existence and quantity of these bacteria.