Listen to what Ron Shimek says... he has done a lab analysis of all the various foods marketed for the marine aquarium hobby. Let's just say he doesn't have a very high opinion of the bottled 'liquid nutrients' commonly sold.
These are his very own words quoted from a thread in RC...
"But the other liquid additives tested, Marine Snow, and Combisan, respectively had almost no or no food value."
Anyway... if you don't trust me about the value of phytoplankton vs Combisan or Marine Snow... just do your own search on the internet and RC.
I only do what's best for my tank after I have done my research.