Dry Chum

I was given a container of dry chum by a guide I went out with. Once I learned to be patient I found it beneficial in castnetting bait. Upon inquiry I learned it was Purina fish food and it can be purchased at feed dealers economically in 50 lb bags. Problem is the feed dealer I spoke to says there are 8 types of Purina fish food. My guide friend dumps the bag into a plastic container and does not know which one it might be. Can anyone please fill in the blank of what type would be used for catching bait in SW Florida?