The invention relates to a method for the cultivation of microorganisms, especially phototrophic microorganisms in a bioreactor or photobioreactor, wherein bicarbonate ions and carbonate ions or a cation surplus concentration in the culture medium is added. The invention also relates to a tubular bioreactor and photobioreactor wherein the method can be achieved and the use of bioreactors, photobioreactors, tubes and pipes in a method according to the present invention.