Abstract: The invention pertains to a system for injecting beneficial micro-organisms into an indoor environment, the system comprising: a container (1) configured to contain a mix of micro-organisms; a nebulizer (9) arranged to spray an amount of said mix of micro-organisms into a ventilation channel of said indoor environment; a pump (4) arranged to transport said amount of said mix of micro-organisms to be nebulized from said container (1) to said nebulizer (9); a flow meter (6) arranged to measure the flow of said amount of said mix of micro-organisms; and a controller (8), operatively connected to said flow meter (6) and said pump (4), said controller (8) being configured to control at least said pump (4) in function of at least measurements of said flow meter.