## 4 Discussion  
Feces and residual feed may decompose to organic suspended solids, which further generate TAN and nitrite, harming breeding animals' health. Suspended solids in the RAS also provide surface area that can be colonized by bacteria. As circulation intensity \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Methods** & **Accuracy** & **Precision** & **Recall** & **F1-Score** \\ \hline \multirow{2}{*}{GA-BP} & 92.14\% (Train) & 95.21\% (Train) & 92.98\% (Train) & 94.08\% (Train) \\  & 86.32\% (Test) & 90.74\% (Test) & 85.96\% (Test) & 88.29\% (Test) \\ \hline \multirow{2}{*}{ELM} & 95.00\% (Train) & 96.41\% (Train) & 95.27\% (Train) & 95.84\% (Train) \\  & 89.47\% (Test) & 91.23\% (Test) & 91.23\% (Test) & 91.23\% (Test) \\ \hline \multirow{2}{*}{PNN} & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) \\  & 71.58\% (Test) & 81.48\% (Test) & 72.13\% (Test) & 76.52\% (Test) \\ \hline \multirow{2}{*}{LSTM} & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) \\  & 96.84\% (Test) & 94.34\% (Test) & 100\% (Test) & 93.83\% (Test) \\ \hline \multirow{2}{*}{GS-SVM} & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) \\  & 97.89\% (Test) & 98.11\% (Test) & 98.11\% (Test) & 98.11\% (Test) \\ \hline \multirow{2}{*}{LS-SVM} & 94.29\% (Train) & 94.22\% (Train) & 96.45\% (Train) & 95.32\% (Train) \\  & 96.84\% (Test) & 96.55\% (Test) & 98.25\% (Test) & 97.39\% (Test) \\ \hline \multirow{2}{*}{CS-SVM} & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) \\  & 97.89\% (Test) & 98.11\% (Test) & 98.11\% (Test) & 98.11\% (Test) \\ \hline \multirow{2}{*}{GA-SVM} & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) & 100.00\% (Train) \\  & 98.95\% (Test) & 98.36\% (Test) & 100\% (Test) & 99.17\% (Test) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of model evaluation indicators for machine learning classifiers. Figure 5: Evaluation indicators of classification models based on machine learning: (**a**) accuracy of the training sets; (**b**) F1-score of the training sets; (**c**) accuracy of the test sets; (**d**) F1-score of the test sets. increases, more particles accumulate, which may increase the bacterial carrying capacity of the system. Hence, rapid removal of solid waste is the most critical unit process in an RAS [34]. The traditional method of water quality regulation in an RAS is to act when water quality deteriorates. This approach leads to large fluctuations in the water environment, and the cost of water quality regulation becomes very high, often requiring many water exchanges to control water quality. This study proposes regulation of RAS circulation based on process control technology, relying on the microfilter backwash times in a unit period (0.5 h) as the main parameter to reflect the overall turbidity of the water body. The variable-flow RAS circulation strategy was designed to form microfilter-circulating pump linkage technology based on water quality parameters and backwash times at different flow rates. An intelligent variable-flow regulation model was developed to keep the water clean and quickly and dynamically remove suspended solids. Related research has proven the significant differences in water quality between the high and low makeup water exchange treatment groups [35]. One study has shown that increasing RAS water circulation can effectively reduce ammonia and nitrite [36]; the higher the circulation level, the lower the ammonia and nitrite mass concentrations became. Moreover, the conversion of nitrite revealed a certain hysteresis, and the ammonia peak appeared earlier than the nitrite peak after feeding was stopped. RAS solids come mainly from uneaten feed and fecal solids, and the decomposition and mineralization of these solids lead to elevated ammonia and nitrite levels in the RAS [10]. Data such as TAN, NO2-N, and TSS must be obtained by manual measurement and are challenging to obtain by sensors. According to [PERSON] et al.