How Do Plants Get Nutrients in Aquaponics.

Students looking over lettuce in an Aquaponics system

Students looking over lettuce in an Aquaponics system

The primary source of plant nutrient in an Aquaponics system is the fish food.  The beautiful thing is that the fish food is a  one source of nutrient for the plants and the fish, a very important principle in working towards sustainability.|

Two uses from the same resource.

It is therefore important to choose a good quality fish food to feed your fish.   There is no magic happening in the body of the fish whereby it can mysteriously produce a full range of plant nutrient from a poor input for it's own needs. It is basic logic that a good quality, balanced fish food pellet will serve the overall Aquaponics system very well.

However, there are three elements that do not come into the Aquaponics easily from the fish food input.
1 Potassium, 2 Calcium, 3 Iron.

Happily, we can supply the Potassium and Calcium to the system when adjusting the system pH upwards.  As you would know, the natural state of affairs in a well found Aquaponics system is that the pH is always slowly drifting downwards, so there is a need to adjust the system pH upwards periodically as required.

Iron is added in the form of Iron chelates as required when the plants exhibit some iron deficiency or on a regular basis , say once every three months.

A good way to provide all the micro nutrients the plants require is to make sure you are running your system with the incorporation of some media beds.  Media beds provide a wonderful environment for the development of what I like to term, a “Nutrient Bank”. Over time we find that there is a build up of fine solids in the media beds, we find that worms take up residence, or we add them. The worms do what worms do to all organic material. They move about in the media bed and process the solids collected there. The solids are reduced in volume by up to 80% by this process and locked up nutrients are released.

Additionally, and very importantly we make good use of our own home-grown compost teas. Every Aquaponics gardener should become a master composter.  The compost tea so produced provides a myriad of plant nutrients for the system.   Compost tea has other important uses in our Aquaponic garden…..but that is the subject of another post.

Find out more about these very important info pieces by attending one of our training programs.

See here for upcoming info and training events.

Aphids in Aquaponics – Control Methods.

Pest Management Methods.


Striped Lady Beetle at work on a Komatsuna leaf. Komatsuna is an Asian style leafy green used in salads and stir fry dishes.

Striped Lady Beetle at work on a Komatsuna leaf. Komatsuna is an Asian style leafy green used in salads and stir fry dishes. See the large aphid to the left bottom of the photo

Aphids are one of the more difficult plant pests to deal with in an Aquaponics fish garden. How do they get into the garden? Usually they are brought in on plants, seedlings that you purchase from a nursery, or carried there by ants from some nearby garden.

Evidently there are around 4000 different types of aphid and at times I am sure most of them have been in my garden at some time!

Controlling them is a little difficult in Aquaponics because we do not have available to us sprayable material such as insecticides that would be commonly used on the regular farm or garden.  We really don't want to use that kind of pest management for a couple of reasons.
1... We want to get away from using dangerous chemicals on our food supply.
2... If we spray that kind of poison we will most likely kill the fish.
3... Poisonous sprays kill beneficial insects as well as destructive insects.

One spray able solution is Neem Oil. This product is an oil extracted from the neem tree which is native to India.  Neem oil is considered to be a non toxic solution and is used as one insect control mechanism on some organic farms.  Neem oil is not very fish friendly so if it is intended to spray this material on your aphid infected plants then great care must be taken to prevent the oil spray drift getting into contact with the water.  This is, in practice, very difficult to do. We spray garlic concentrate, chilli spray, molasses spray regularly in summer but find that these methods help but are not nearly as effective as the use of beneficial insects.


Aphids can be seen on the leaf (white insects) and in the middle the predatory wasp Aphidius ervi can be seen.

The best way to control aphids is by the use of “IPM” or Integrated Pest Management. IPM aims to suppress pest populations below the economic injury level (EIL)[i]
Seen here is an aphid infestation that is under attack by parasitic wasps Aphidius ervi
These wasps are multiplying rapidly to cope with the aphid infestation.

In keeping with the underlying mantra of our Aquaponics Garden being an ECO system it would be counterproductive to find some poison to kill the aphids for example, because at the same time we would very likely also despatch any beneficial insects. Particularly threatened by these "poison" approaches is the honey bee, and all would agree that would be disastrous.

The most "all purpose" beneficial insect is the Green Lacewing.


Green Lacewing. Photo by Wikimedia

As the common name implies, adult green lacewings are green, with four clear wings. Adult female lacewings live for approximately three or four weeks and lay up to 600 eggs. The eggs hatch and the insect goes about its task of dealing with a variety of garden pests such as,
Aphids (various species)
Twospotted mite Tetranychus urticae
Greenhouse whitefly Trialeurodes vaporariorum
Scales (various species)
Mealybugs (various species)
Moth eggs and small caterpillars


Lacewing Larva doing a job on an aphid.
Photo "Bugs for Bugs"

So they are pretty handy to have around the greenhouse.

These can be purchased fairly inexpensively and do a great job.   Visit the “Bugs for Us” website for detailed information on how to purchase these little critters and release them in your garden or farm.


Striped Ladybird Beetle - Micraspis frenata

Striped Ladybird Beetle - Micraspis frenata

Here is another insect that we have in our Indy 23 greenhouse doing its share of work on the resident aphid population.
The Striped Ladybird Beetle.

There are 27 main groups of this little beauty that are a very important part of our Integrated Pest Management approach in Aquaponics gardening either for home or in a commercial farm setting.

Striped Ladybird Beetle Photo by Brisbane Insects

Striped Ladybird Beetle
Photo by Brisbane Insects


See more info about these wonderful little creatures at Brisbane Insects.





[i] "AGP - Integrated Pest Management". Retrieved 21 August 2013.