I have an aquaponics system with 20 Koi fish and different plants which works by the Siphon method , and the fish water is about 22-26°c, which is usually less for plants of 2°c degrees. The water is constantly pumped and rotated in the system, and the plants are constantly in the water. Oxygen and three filters are always working in fish tank, and I used synthetic light for the plants in low sunlight hours. I add nutrient and potassium solutions and vitamins in the system, but unfortunately plants and vegetables are after a few days ,or dry their leaves or shedding flowers exp. (tomatoes, cucumbers and green beans ...)

I really do not know what is the problem ? and what should I do? I am thankful with your guidance. enter image description here

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EDIT: I think I found the answer to my question, the water hardness of my system is over 21 (GH>21)=425, in your opinion, could this cause me sluggish plant growth and low fertility and plant destruction?

  • 3
    I believe this would be a better fit on Gardening.SE -- there appear to be a number of good questions and answers on aquaponics there.
    – LShaver
    Feb 14, 2018 at 15:35
  • I'm not sure what you mean by the siphon method. Do you mean that the top water level in koi tank is higher than the drain in the planting bed. You need powered flow at some point.
    – That Idiot
    Feb 14, 2018 at 18:36
  • I suspect he means flood and drain using bell siphons Mar 11, 2018 at 19:38
  • Would love to hear whether you got your problem solved... Mar 11, 2018 at 22:12

1 Answer 1


To determine if lighting levels are responsible, I suggest you put similar plants (tomatoes, cucumbers and green beans) into self-contained pots (using potting mix) and sit them within the same lighting as what the aquaponics system gets, and see how well they grow. You will of course need to water them manually as appropriate.

It may also be worth double checking that you've added the nutrients at the correct concentration for the system.

  • Thanks.Should we use supplementary nutrients in aquaponics?
    – farnaz
    Feb 15, 2018 at 21:19
  • @farnaz That's not something I can answer, sorry! Feb 16, 2018 at 0:58
  • You might need potassium and iron supplementation. But this question belongs to gardening which covers this topic. Mar 11, 2018 at 19:41

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