There are three general methods to grow algae that are across a spectrum. Batch culture, semi continuous batch culture, and continuous culture.
In the batch culture your have a finite volume of media in which the cells grow. You do not add any new media. Over time the biomass looks like this plot. The culture experiences lag-phase, exponential growth, stationary phase, then decline.
In the semi-continuous batch culture. The culture is harvested every day to week and new media is added to the container. For the greatest amount of biomass produced, the harvesting is done at the highest biomass possible before the culture enters the stationary phase of growth. The culture experiences the lag phase and exponential phases. If done correctly, it never entered stationary phase or decline. Over time this type of culture method could experience pathogens or weed algae growing in the media, so monitoring of the culture is important.
A continuous culture is a most efficient way to create biomass. This culture method is also called a chemostat, or a turbidostat (when the density is held constant). In this method, a continuous supply of media is added to the culture. With the culture volume held stationary, every new mL of media yields a new ml of product. You could view this a semi-continuous batch culture, where the harvest phase is every second.