FTW as a wastewater processing technology in recirculating aquaculture systems (RAS) of catfish is considered to be effective in eliminating the pollutant load of nitrogen, phosphorous, and organic matter. This research aims to reduce the concentration of pollutant loads and obtain an effective ratio between the volume of the FTW and the total water volume of the catfish RAS. The FTW system uses Vetiveria zizanoides grown on floating media and equipped with an aerator in the bottom layer of the pond. Several FTW volume ratios were used to determine an FTW system that is effective in reducing pollutant loads according to the mass balance concept. This approach was conducted to maintain acceptable water quality in catfish cultivation ponds. The study results showed that most pollutant load concentrations decreased in all ponds. The largest removal percentage included the parameters TAN, COD, TSS, TP, nitrate, phosphate, and TN, namely 88.54%, 49.35%, 85.68%, and 91.30%, respectively. The effective ratio between the volume of the FTW processing system and the total water volume of 0.543 and 0.725.