i thought you were talking about the brightwell brand reef snow lol. well in the ocean marine snow is pretty much any organic matter i.e. zooplankton, pyhtoplankton, sperm and eggs from fish and inverts, that inverts can feed off of most of the time its the stuff that dies and falls/gets blown onto the coral or whatever thats going to eat it because usually the live stuff will stay up in the water colom because they have some form of motility. anyway to answer your question it depends on what you want to feed. there several diffrent brands and sizes of things that would fall into the "marine snow" catagory. some corals like smaller food because either their mouth is too small to eat bigger stuff or they cant prperly grab it to pull it into the mouth. and some prefer bigger food. if youre looking to feed a varity of diffrent things get something that has a large range of sizes. for example brightwells zooplanktos-M has particles ranging from .5 to 1 Kµm and most products should have a particle size listed on the bottle