During the growth of population in the world, Recirculating Aquaculture Systems (RAS) are developing due to more production and less water consumption and many scientists have studied on water quality and solid removal at these systems. In this paper to study on settling pattern of solid particles on a bed of aquaculture cylindrical tanks, a tank in diameter of 2.14 m and height of 0.59 m and inlet flow using three nozzles in 8 mm diameter has implemented. Quality and quantity studies of settling patterns of solid particles in six injection location (by changing the injection location of radial alignment for three options and on the pyramid of tank for others) show that injection location by the middle location of radial length and of third station (there are 6 stations on the pyramid of the tank and each station has located at 60 degrees from the last station) created more uniform sedimentation on the bed. Also, laboratory observations show that the low density materials such as fish feed, which has a high rate of immersion are more disposed to exit due to spiral flow of cylindrical tanks.
)