Hi, you can find different understanding in literature of what is meant under Redfield ratio. Correctly it is the generally observed ratio of 106:16:1 C:N:P in oceans (A. Redfield 1934) as you mention it. But sometimes people refer to "Redfield ratio" as any C:N:P, which is confusing, of course. Many organisms (and your Chlorella obviously..) can depart quite far from this probably optimal macronutrient ratio established on a geological time scale by cycling between the marine phytoplankton cells (with their nutrient requirements for photosynthesis and proteosynthesis cell machinery) the marine sediments and the continental crust. It's an exciting observation and an excellent question! For more info about the particular mechanisms driving the C:N:P ratio I can recommend the book Ecological Stoichiometry (Sterner & Elser, https://press.princeton.edu/books/paperback/9780691074917/ecological-stoichiometry)