<![CDATA[The growing demand for efficient, water-conserving, and sustainable aquaculture systems has accelerated the development of recirculating aquaculture system (RAS) technology. Although RAS can reduce water use by 90–99% compared to conventional systems, challenges remain related to metabolic waste accumulation and energy requirements. Therefore, this study aims to: (1) evaluate the effects of water change (25% and 50%) and filtration on water quality and water use; (2) assess system performance based on energy consumption and operational costs; and (3) determine the most efficient configuration for grass carp (Ctenopharyngodon idella) culture. The study was conducted at the Terpadu Laboratory, IPB Dramaga Campus, Bogor, using a completely randomized design (CRD) with three treatments: 25% water change (WC25), 50% water change (WC50), and a filtration system without water change (FS). Water changes were applied when water quality parameters exceeded predefined thresholds. Water quality parameters (ammonia, nitrite, nitrate, temperature, dissolved oxygen, and pH) were monitored daily, while water use, energy consumption, and operational costs were recorded and analyzed. The filtration system (FS) was the most effective in maintaining water quality, reducing ammonia from 2.25 mg/L to 0.25 mg/L, nitrite from 0.15 mg/L to 0.01 mg/L, and nitrate from 80 mg/L to 25 mg/L. FS also demonstrated the highest water use efficiency, consuming only 5 m³/month with a water cost of IDR 30,055. Although energy consumption was slightly higher, FS resulted in the lowest total operational cost (IDR 969,667/month). The integration of a filtration system in RAS is more effective in maintaining water quality, reducing water consumption, and improving economic efficiency compared to water change strategies, making it a suitable approach for sustainable grass carp aquaculture]]>
