Graber and Junge (2009) reported that an important lack in fish
water was its low potassium concentration, which was 45 times
lower than in hydroponic. This resulted in a poorer tomato quality
in aquaponic compared with the hydroponic production system.
Potassium limitation was reflected by fruit analysis; aquaponic
tomatoes contained 22.0gKkg−1 dry matter versus 40.8gKkg−1
dry matter in hydroponic. Therefore, high effects of foliar application
of K on cluster number, fruit number and yield of tomato in
our experiment have been due to low amount of K in fish water