rsteagall,
I've heard that also, but I don't know that I'd rely on it. I'm thinking that they probably do control them to some extent but that you most likely need a whole bunch of it to really have a significant effect (and a bigger effect than other ways of controlling nitrates). Then again, maybe I'm wrong about that and the next thing we'll see in the hobby is dedicated xenia growing areas in sumps. Anyone have any science on this?