It has been a very hard problem to reduce solids especially suspended solids (SS) in recirculating aquaculture systems. Present description is based on the performance of trapping SS by the biofilter of Intensive Bio-production Korean (IBK) system which is originally developed for nitrification. We found out that this filter has an excellent capability to remove SS in addition to nitrification. Filter element used here is corrugated plastic roofing plates readily available in the market, and cheaper than specially developed and patented products. It is easy to maintain the system, and requires low power consumption to operate for the treatment of a large amount of water. With 2 pumps of 5 hp each, about 500 $m^3$ of water is treated per hour. Flow speed in the filter was 2.6 mm/sec on average. This low flow speed and very large amount of water treated are the reasons for very effective trapping of fine SS. Upon single pass through this filter, 74.5% of total SS and 40% of non-settleable SS were removed. Wherever this filter is employed in recirculating fish farms water keeps high clarity, this having also been empirically ascertained.