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 ...)
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?