Guillard's f/2 formula growth medium standard for over 30 years Essential to pre-loading vitamins into phytoplankton prior to feeding fry Promotes the highest cell densities in your phytoplankton culture Contains no silicates Mercer Of Montana has concentrated the Guillard f/2 formula to help you achieve high density, continuous or batch cultures of micro algae for your fish fry, rotifer and artemia feed, or to dose to your aquarium system. Hydro Algal Fertilizer, Phyto Pheed, has an extended shelf life, and using the suggested dosing of 1ml/liter, one 8 ounce bottle will last.