An apparatus for growing biological mass has a container for accommodating a biological mass in liquid to be grown in presence of light, a plurality of light sources in an interior of the container, a first movable plate which has passages for the light sources and which is reciprocatingly movable along the light sources to clean the latter, the first plate also having a first openings permeable for the liquid and for the biological mass, and a second plate located under the first plate and configured so that it is permeable for water and small algae fraction which have still to be grown but not permeable for the biological mass with fully grown algae, so that for discharging the biological mass the first and second plates are placed over one another and together moved toward a discharge so that the water can pass through both plates, while the biological mass is held on the first plate and moved toward the discharge to be discharged outwardly.