The increased use of Recirculating Aquaculture Systems (RAS) makes the development of cost-effective components essential. This paper describes the innovative use of widely available Intermediate Bulk Containers (IBC) as part of a fluidized bed biofilter. Four, 946.4-L IBC units, with tops removed, were filled with K1 style media to approximately 92% media-to-IBC total volume. A regenerative blower to push 2,718 L/min of air at a pressure of 12.46 kPa through two diffusers to fluidize the bed in each IBC unit. Flow rates through the entire system was 303 L/min, or approximately 75 L/min through each IBC unit. The biofilter was evaluated in two trials during rearing of larval walleye (Sander vitreus). Trial one included 640,000 larval walleye, temperatures ranged from 17.5°C to 23.6°C, ammonia levels reaching 0.59 mg/L, feeding rate of 12.4 kg/day, and pH of 7.5. Trial two included 480,000 larval walleye, temperatures ranged from 17.5°C to 22.5°C, ammonia levels reaching 0.70 mg/L, feeding rate of 14.9 kg/day, and pH of 7.2. Based on these results and additional rearing experiences, this Fluidized Bed Biofilter is suitable for production level rearing of fish in RAS.