Aquaponics 6: Get the little things right

Photo: Kleinskuur Aquaponics

In this last part of the series on aquaponics we focus on the little things that can become big things if not attended to. Very often new aquaponic farmers setting out to conquer the world have spent so much time, energy and research on sourcing material and building their systems that they forget they still have to farm once everything is up and running.

An aquaponic system is a production method; nothing less, nothing more. It will not do the farming bit for you. You still need to do everything any other farmer is supposed to do, with the difference being that you can expect much better yields from an aquaponic system compared to planting in soil or even hydroponics. Remember you have fish to sell.

Caring for your tilapia

Fish are generally happy if they have clean, aerated water of the right temperature, and enough good food. These are the basics you need to get right to be a successful fish farmer.

Clean water: Borehole water is usually the best source of water to use in a system, but before you start any farming enterprise on any piece of land, have your water tested! Make sure that it is not too brackish or contain pollutants.

Tilapia are quite tough, more so than other species, but your purpose is to make things as easy as possible for them to let them grow as quickly as possible so that you can make money from selling them. The cleaner the water, the faster they will grow. It also means that you need enough plants in the system to clean the water before it flows back to the fish.

Aeration or oxygenation: If you keep a lot of fish in a small area, you need to add air into the water. A blower pushing air through some air stones should be adequate. The purpose of the air stones is to supply the air evenly and in smaller bubbles. A big bubble tends to float up to the surface and break into the air, adding very little oxygen to the water.

There are also farmers who add a little air pipe onto the main water inflow pipe which draws the air into the stream of water falling into the dam. It can work very well if your dams are not too densely populated – less than 30 fish per 1 000 litres. If the inlet water breaks the surface of the water, it will also add to the oxygen levels.

On the other extreme I have seen fish farms with seriously big oxygen tanks, adding pure oxygen to the water, which I am sure is very effective and also very expensive. I have never seen an oxygen tank in nature. The fish in rivers and big dams seem to be doing okay without humans adding oxygen to the water.

In nature, the large surface areas of water and the fact that water moves over stones in rivers see to it that there is enough oxygen in the water. Of course, the water is not as densely populated as in a commercial fish tank, which is why we need to add air.

If you notice that your tilapia are all swimming close to the surface, they are probably coming up for air. Check your air flow!

Water aeration system. Photo:

Temperature: In Zambia the water temperature is mostly suited to rearing tilapia without adding heat. If you are in an area where the water temperature drops below 16˚C in winter, you need to heat up the water, because your fish will not grow and may even die. The ideal is to keep the temperature above 23˚C at all times and if you can keep it at 28˚C, your fish will thrive, even through the winter.

If you have your own hatchery, it is particularly important to maintain a steady high temperature for the breeding pairs, eggs and young fish.

There are water heaters available, which should work well in smaller tanks, as in the hatchery, but it will devour electricity and add to your expenses.

Some farmers use a furnace or wood burner to heat the water as it circulates, which works quite well if you have sufficient labour and wood. Circulating water through black pipes to catch the heat of the sun will work during the day, but the process may be reversed at night, cooling down the water instead of heating it up.

If you know you are going to have a problem in winter, make sure your system design includes a covered and insulated area for the fish. If you can control the air temperature, you can decrease the dropping of water temperature at night. Just remember the water can also cool down in the plant section, so it may be necessary to adjust your water flow at night.

The Kleinskuur Aquaponics design includes a geothermal heating system with a heat pump, which is initially expensive and uses electricity, but a lot less than heaters, saving you money in the long run.

If your fish are keeping to the bottom of the tank and do not eat, check the water temperature. It is probably too low.

Inline water heater. Photo: elecro.

Enough good food: In last month’s article we explained how to work out the ratio between fish feed and the number of plants you can have in your system. A tilapia needs to eat 1% of its own weight every day. Small fish obviously eat less than big fish, so if you have mixed sizes in one tank you need to get an average weight. Weigh ten fish of the different sizes and get the average. But remember that small fish need small flakes and bigger fish need bigger pellets.

The best way to determine what type of feed, size of pellets and amount of feed your fish need, is to ask for advice at one of the excellent fish feed manufacturers in the country. You will find their advertisements in ProAgri Zambia. They have all the formulas at hand.

At Kleinskuur we supplement the fish feed with duckweed, but be warned, once you get duckweed into your system, it will stay and multiply, also using nutrients.

Remember that the nutrients your plants need start with your fish feed. Get the best fish feed possible. It will be your largest operational cost, but the income from the fish should already make up for it.

Black pipe heating spiral. Photo:

Caring for your plants

Plants basically need the same things your fish do, namely clean, aerated water of the right temperature, and enough good food. That is why the fish and plants work so well together.

Clean water: Plants also thrive in clean water. Many people have this idea that you keep the fish and the plants in the same dam and then everything happens by itself. Although we emulate nature, an aquaponic system is a man-made production system and we need to control certain aspects.

One of them is “cleaning” the water coming from the fish. This means taking the solid fish waste and uneaten food out of the system. By leaving it in you will create pockets of anaerobic bacterial growth and clog up the pipes and pump. Solids should be mineralised by adding a compost activator (a concentration of good bacteria) and lots of air, after which the mineral rich water can go back into the system.

The other part of cleaning is filtering the water through the bacteria system which converts the ammonia the fish breathe out into nitrites and then nitrates – your plant food! This is called nitrification.

The water should circulate properly throughout the whole system to keep it clean for the plants as well. If you have stagnant areas it will encourage anaerobic bacteria reversing the nitrification process.

Healthy cos and fancy lettuce in the Kleinskuur Aquaponics system.

Aerated water: The plant roots also need air to grow, whether they are in the soil or in water. You can use the same blower in your fish system (if it is big enough) to add air to your deep-water culture plant section with the help of air stones or air lines.

There are people who believe that splashing water from a height breaking the surface will add enough air. At Kleinskuur we have air lines with little holes running along the bottom of the water beds.

Temperature: Most plants are happy if the temperature around their root zones is 23˚C, even if the air temperature drops or increases. If you farm with cold water fish species, like trout, you may need to heat up the water for the plants. With tilapia you are safe both ways if you can keep the water at 23˚C.

Enough good food: As explained above, the nutrients your plants need start with your fish feed. You want your fish to grow, breathe and poo; then your plants should be fine.

Three elements you will need to add is iron, potassium and calcium, but don’t overdo it. In our system with 280 000 litres of water and around 18 000 plants we add 5 to 7 kg of each every week.

If you can have your water and leaves tested for nutrients, wonderful! If you can’t, make sure you get a leaf chart on the internet showing you the symptoms of shortages. Also remember that the pH of the water should be around 6,5 for all the nutrients to be taken up optimally.

Praying mantis eating a grasshopper. Photo:

What about insects?

One of the questions we get asked most is about handling harmful insects. You will get mean little buggers coming in to eat your plants. You cannot kill them with chemicals as your fish will die and so will your system.

If your plants are young, healthy and strong, insects should not be a big problem. Luckily the natural enemies of these mean little buggers are bigger, meaner buggers. Did you know that a lovely little ladybug grabs and holds her prey, bites its head off and sucks the juice out of the rest? And she can eat hundreds of these every day…

A praying mantis is top of the range in killing little buggers, and dragon flies are some of our best friends. Their larvae live in the water devouring any wannabe mosquito. It is a jungle out there!

If you have a closed net house, you will be able to keep out most of the flying plant eating bugs and if they do become a pest you can really mail order in some ladybugs.

Fungus infections and powdery mildew are some of the things you need to look out for in high humidity places at times. Destroy the affected leaves or plants, make sure there is enough air around the leaves of the remaining plants by thinning them out.

There are biological treatments available if you have a crisis, but make sure they have been tested on fish. It may not be harmful to humans, but can have an oily base clogging up the gills of the fish!

We once had to resort to the drastic measure of spraying lemon juice on our basil! It killed the aphids and added an interesting flavour to the basil.

The purpose is to produce healthy, good looking food, but if you find a worm on a spinach leaf, relax, it is a clear sign that it is safe for human consumption.


Should you wish to find out more about the economical side of aquaponics you can download an e-book called Aquanomics, building a thriving aquaponic business, co-written by Kleinskuur Aquaponics and Hydrotower. Get the e-book at:

For more information on aquaponic systems visit

Dragonfly nymph eating a mosquito
larva. Photo:

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