1.1 ,This practice measures by Pseudokirchnereilla subcapitata growth response, the biological availability of nutrients, as contrasted with chemical analysis of the components of the sample. This practice is useful for assessing the impact of nutrients, and changes in their loading, upon freshwater algal productivity. Other laboratory or indigenous algae can be used with this practice. However, Pseudokirchnereilla subcapitata must be cultured as a reference alga along with the alternative algal species.