A container arrangement (1) for fish farming comprising a body (3) with a bottom section (5) and a wall section (7) that define a volume adapted to receive water (10) for the fish farming, and a water treatment arrangement (20) for treatment of the water (10) in the container arrangement (1). The water treatment arrangement (20) comprises a device (24) for removal of CO2 from the water (10) of the container arrangement (1) comprising a separation chamber for CO2 and means for separation of CO2 arranged at said chamber, and which water treatment arrangement (20) is arranged in the body (3) of the container arrangement (1).
