Effect of Inorganic Substrates on the Water Quality and Growth of Kalanchoe blossfeldiana in an Aquaponic System

Substrates are important for plant growth as they maintain the water quality in an aquaponic system. The aim of this study was to investigate the effects of four inorganic substrates of sponge (SS), orchid stone (SO), hydroball (SH), and volcanic rock (SV) on an aquaponic system for planterior (use of plants in interior design) purposes. A recycling deep flow system was used. Kalanchoe blossfeldiana 'Peperu' seedlings and goldfish (Carassius auratus auratus) were kept together for 50 days in a small tank divided into two sections. Every day, 0.25 g of fish feed was supplied into each tank. The electrical conductivity (EC) and pH of the water were checked regularly. The nutrient concentration of the aquaponics water and the plant growth parameters were measured. The results showed that the increasing pattern of the EC strength over time was identical under the different treatments. The pH of the water fluctuated with different ranges for each treatment. Furthermore, the NH4+ concentration in aquaponic water increased sharply from 15 to 20 days in all treatments, later becoming more stable. The NO3- and Mg2+ ion concentrations also sharply increased after 15 to 20 days of treatment; later, NO3- was found to have increased in the SH, SS, and SO treatments. However, at 35 days after treatment, Mg2+ and Ca2+ showed a similar stable concentration trend in all treatments. An inverse relationship was observed between the Ca2+ and HPO42- concentrations in all treatments. Plant heights, widths, and stem diameters of K. blossfeldiana were not significantly different among the treatments. The number of leaves, the leaf length, and the leaf width of the plants were also not statistically different among the treatments. At 50 days after the commencement of treatment, the SPAD value of plants was higher in the SH treatment than in the others. Furthermore, the numbers of branches, nodes, and flowers of plant were not significantly different among the treatments. These results indicate that the inorganic sponge, orchid stone, hydroball, and volcanic rock substrates influenced the EC, pH, and ion concentrations in aquaponics water. In addition, the period of the first 20 days is crucial to ensure stable ion concentrations in water. However, these substrates did not significantly affect the growth of K. blossfeldiana.