Journal of Great Lakes Research 36(3): 540-547 (2010)
With the help of modern human transportation, invasive species can reach habitats that they never could before. The ballast water of ships carries multitudes of microorganisms that, when discharged into a new ecosystem, can disrupt the natural balance in that area. Experiments done in the Laurentian Great Lakes concluded that assemblage, staining, and observation was the most efficient way to evaluate the freshwater organism content in ballast discharge while other methods proved ineffective and unclear.
Euan D. Revie and his research team from the University of Minnesota Duluth tested multiple ballast water treatments, such as: enzyme digestion, flow cytometry, and multiple stains. A reliable process to test the densities of phytoplankton cells in the 10-50 micrometer range has yet to be found, and reliability was based on several factors. The methods were tested for precision of the organisms’ conditions at ballast water discharge, consistency of results in a given area, and practicality as well as speed of method during on-site projects.
It is a little unclear in the second paragraph as to what you mean. You say that neither enzyme digestion, flow cytometry, or multiple stains are an effective way to test ballast water. But in the first paragraph you say that assemblage, staining, and observation are the most efficient way. Do you mean that although none of them are very effective, that is the best way to do it? It might help just to make sure the reader understands the point of the article.