f/2 Fertilizer, for those culturing or looking to culture their own Phytoplankton! This fertilizer is the standard in phytoplankton culturing, and is specifically formulated for it, so it will not leave you with a “dirty” culture as something like Miracle Grow would.$20 for a 475ml bottle, 1ml making 1.25L of Phytoplankton. Plus a syringe. One bottle being good for almost 600L of Phyto!