And lots of corals and filter feeders eat dissolved organic compounds and fine particulate detritus. Lots of things are extracted from the water that is why it is nice to innoculate your substarte with live sand from several sources as well as getting live rock from several sources. Lots of people, several times each year, reinnoculate their tanks with purchased innoculation packages and small amounts of live sand and live rock from healthy well established tanks. Reefers with well established deep sand beds are good people to know, as are people with old refugiums with deep sand or mud beds.