## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Off-Flavors**} & \multicolumn{4}{c}{**Aquaponics**} & \multicolumn{2}{c}{**Hydroponics**} \\ \cline{2-6}  & **Start** & **End** & **End** & **End** \\ \hline \multirow{2}{*}{MIB (ng/L)} & shoot & 1079.4 & 704.4 & \(\pm\) 73.08 \({}^{\text{Aa}}\) & 278.00 & \(\pm\)158.2 \({}^{\text{Aa}}\) \\  & root & 1260.6 & 1496.6 & \(\pm\) 998.2 & 300.50 & \(\pm\) 80.48 \({}^{\text{A}}\) \\ GSM (ng/L) & shoot & 134.4 & 8.68 & \(\pm\) 2.50 \({}^{\text{A}}\) & 7.87 & \(\pm\) 2.24 \({}^{\text{A}}\) \\  & root & 212.8 & 3579.8 & \(\pm\) 1682.8 \({}^{\text{A}}\) & 191.80 & \(\pm\) 48.78 \({}^{\text{A}}\) \\ \hline \hline \end{tabular} Values are means \(\pm\) SD, \(n=3\), \(p<0.05\), The superscript letter \({}^{\text{A}\times n}\) indicates statistically significant difference (\(p<0.05\)) between the sampling points and \({}^{\text{A}\times n}\) between the treatments (aquonics vs. RAS).  
\end{table} 
Table 7: Concentrations (ng/L) of off-flavors geosmin (GSM) and 2-methylisoborneol (MIB) in spinach grown in aquonics and hydroponics in the beginning (5 May) and after six weeks (14 June) of the experiment. of unionised ammonia of TAN increases with the increase in pH and temperature [1]. The concentrations of TAN, nitrite, and pH should be adjusted if they are outside the acceptable limits [1]. Aquaponics systems are beneficial in terms of low water use, nutrient recycling, and improving the quality of the recirculating water [41; 42]. In the present study, we found that the first step of nitrification (oxidation of TAN to nitrite) started slightly faster in aquaponics treatment than in RAS. TAN levels rose at the beginning of the experiment in both treatments and then gradually decreased, and there was no significant difference between treatments in TAN concentrations. The daily mean concentration of TAN decreased below 1 mg/L (0.67 \(\pm\) 0.58) on day 9 in aquaponics treatment while on day 11 in RAS. For the second step of nitrification (oxidation of nitrite to nitrate), the peak concentration of nitrite (4.83 \(\pm\) 0.14 mg/L) in aquaponics was reached on day 7, while it took 11 days longer in RAS (4.83 \(\pm\) 0.28 mg/L). After day 11, the concentration of nitrite became nearly zero in aquaponics, while in RAS similar concentration was attained in 34 days. Before the nitrification process was properly established, TAN and nitrite were much above the recommended levels [1]. However, these levels did not seem to induce mortality or other negative effects on fish, as seen as good growth and low FCR. This suggests that rainbow trout has a relatively high short-term tolerance for TAN and nitrite. The lower concentrations of TAN, nitrite, and especially nitrate in aquaponics treatment clearly showed that the aquaponic systems worked as expected [43]. This was demonstrated by the plants absorbing all these dissolved nutrients from the water. [PERSON] et al. [27] studied the water quality and productivity of the spring onion (_Allium fistulosum_), lemongrass (_Cymbopogon citratus_), and largemouth bass (_Micropertus salmoides_) juveniles in both RAS and aquaponics. They reported no significant difference in TAN, nitrite, and pH between the treatments. However, nitrate increased steadily in both treatments, although still at a higher level in RAS than in the aquaponic system. In our experiment, the nitrate level remained lower in the aquaponics treatment compared to the RAS treatment. The sudden drop in the nitrate level after day 37 in RAS can be partly linked to water changes as 40-50% water of the system was changed twice in RAS treatment during week six due to the decrease in pH; however, water change cannot be the only reason for this unexpected drop of nitrate level below 5 mg/L (Figure 1c, Table 4). In our study, the pH remained nearly neutral and only slightly different between treatments until day 30. After day 30, there was a sudden decline in pH in RAS treatment.