I have a big problem with green residue clogging fixture screens. There has been no recent(for the last 2 years) plumbing work in the house so it is not flux/solder residue. I have two 50 gallon tanks in series. It appears much worse on the hot water side. I am beginning to think it is a recirculation line coming of the second tank. Because that line's supply comes from the bottom of the tank I think it may be spreading settled matter from the tank.