Decoupled aquaponic systems are gaining popularity as a way to manage water quality in aquaponic systems to suit plant and fish growth independently. Aquaponic systems are known to be deficient in several plant-essential elements, which can be affected by solution pH to either increase or decrease available nutrients. To determine the effect of pH in a decoupled aquaponic system, a study was conducted using aquaculture effluent from tilapia culture tanks at four pH treatments: 5.0, 5.8, 6.5, and 7.0, used to irrigate a cucumber crop. Growth and yield parameters, nutrient content of the irrigation water, and nutrients incorporated into the plant tissue were collected over two growing seasons. pH did not have a practical effect on growth rate, internode length or yield over the two growing seasons. Availability and uptake of several nutrients were affected by pH, but there was no overarching effect that would necessitate its use in commercial systems. Nutrient concentrations in the aquaculture effluent would be considered low compared to hydroponic solutions; however, elemental analysis of leaf tissues was within the recommended ranges. Research into other nutrient sources provided by the system (i.e., solid particles carried with the irrigation water) would provide further information into the nutrient dynamics of this system.

Using aquaculture effluent (AE) to fertigate plants is gaining popularity worldwide. However, in substrate-based systems, the choice of substrate is essential due to their effects on crop productivity. Differences in the retention of nutrients by substrates makes it necessary to assess suitability for use in AE. This study was conducted from January to July in 2016 and September to October in 2019 to evaluate greenhouse-grown Beit Alpha cucumber (Cucumis sativus L. ‘Socrates’) performance fertigated with AE in pine bark or perlite substrates, grown either as one plant or two plants per pot. A 2 × 2 factorial arrangement in a randomized complete block design with four replications for each season was used. The substrate effect on yield in 2016 depended on the density and season. The pooled yield over seasons in 2016 showed pine bark had a significantly higher yield than perlite by 11% in one plant per pot but lowered by the same amount in two plants per pot. In 2019, pine bark significantly reduced the leachate pH in both plant densities and reduced the leachate EC by about 15% in two plants per pot. The foliar boron was occasionally below sufficiency whilst manganese was above sufficiency in pine bark due to its inherently low pH. We conclude that the effect of the substrates on cucumber yield fertigated with AE is dependent on the season and the number of plants per pot. Therefore, due to the local availability of pine bark, it could be a potential substitute for perlite especially when using one plant per pot for AE. In addition, pine bark could be used as an intermediate substrate to reduce the pH in AE for downstream use.