well... that was fast: Mr Tagrin from DT's replied promtly to a request for information.
his comments are pasted below here.
He has also shared a reference from Guillard who developed the F/2 formula and is with the (CCMP) Center for Culture
of Marine Phytoplankton! (next posts)
interesting reading:
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At DT's Plankton Farm; we use advanced cell separation technology that was developed to harvest live, undamaged cells. This is a long, tedious, and expensive process. This same process is used to wash the cells by repeatedly adding and extracting clean saltwater. This product was developed specifically for use in the closed system environment of reef aquariums.
In contrast, centrifuging phytoplankton is a process used by some companies to make algae paste for commercial aquaculture. This process was not designed to harvest live cells and in fact, the cells are scraped out like clay. This method is fast and cheap, but it damages a large percentage of cells. Several companies are purchasing these algal pastes as frozen concentrated phytoplankton to use as ingredients in their marine aquariums
products.
Another concern in any phytoplankton product is unwanted elements resulting from the growth medium. Our concentrating process utilizes a cell washing procedure to remove nutrients and metals that are necessary to culture phytoplankton. This procedure is done by repeatedly adding and extracting
clean saltwater to remove most of the residual culture media. Nutrient removal is necessary because high nutrient levels in packaged live phytoplankton will cause bacteria blooms that will kill off some of the live phytoplankton, and quickly degrade the product while in storage. Furthermore, high levels of dissolved nutrients that contribute to unwanted algal growth.
Metals are removed to keep them from building up in reef aquariums. While many growth media exist, most phytoplankton culture media contains; ferric chloride, EDTA, cobalt chloride, zinc sulfate, copper sulfate, manganese chloride, and sodium molybdate.
While the potential harm the buildup of these chemicals may have is debatable, not knowing their potential detriment is enough reason to avoid repeatedly adding them to the small closed
system volume of a reef aquarium.
Culturing phytoplankton may be a good option if you are using
phytoplankton to raise zooplankton, or for fish culture. The effectiveness and addition of growth media used may depend on the culture, and their result in a reef aquarium may be variable, depending on the culturist. However, our efforts at cleaning phytoplankton are done to make it as safe as possible for
long term use directly in a reef aquarium.