According to the Redfield ratio, microalgae will need roughly 6 times more carbon than nitrogen. For marine species the carbon requirement in small batch cultures is met by the 2 mM contained within seawater, and by allowing atmospheric exchange then the carbon requirement can be supplied over time. Carbon may be lost directly after autoclaving, therefore it is sensible to allow freshly autoclaved media to stand for at least 1-2 days before innoculating with microalgae. Large batch cultures, generally greater than 500 mL to 1 L may need to be aerated with either air or an air/CO2 mix to prevent carbon limitation. Typical CO2 concentrations are in the range 0.5 – 5.0 % v/v.