Phytoplankton
Phytoplankton is a single cell algae plankton that is the base of all life in our oceans

it is a food source for marine creatures such as
Clams
Feather duster worms
Corals
It is also believed to be the only diet of some gorgonians and Dendrophyllia sp
Feed as per the dosing instructions on the label and it will keep in the fridge for up to 6 weeks!
Your skimmer will remove Phytoplankton from the water so you may see some green in the skimmer - but do not worry, this is perfectly normal. 

Primal seas spend a lot of time and money to make sure you get nutrient enriched Phytoplankton not weak uncured water.