I did a side-by-side comparison of most of the plankton foods on the market that came out in the
Marine Fish and Reef USA 2002 Annual. Basically DT's did the best, but I do into a lot more detail in the article. Weiss Co. disagreed with the tests and asked that his products not be included with the results. There is an archive of many of my posts about phytoplankton products available online
here, if you're interested in more detail.
I also explain how to culture phytoplankton, and why sterile technique is important in the GARF archives
here. Basically, if you follow the technique rayjay recommends, you're almost guaranteed that it will not be the species of phytoplankton you think within a few generations. There are plenty of greenwater cultures that are easy to grow, but the nutritional value of unknown species of phytoplankton cultured on plant food is highly variable (although it's fine if you just want to grow brine shrimp like rayjay)....
Rob