The tank in which I have mine is so strongly structured, that I hardly ever see them - there for I also don't see them eat. I throw some pleco chips in along with the regular fish food from time to time, but I don't know if they really eat it. I jut know that they are in good condition and I have seen them poop - so they must eat something...
I dont think they eat fish crap, as I don't think any other fish does. I also don't see mine chow down anything.. I already housed them in the pond with a couple of midsize plecos and with lots of driftwoods. I dont see them feed unlike the others but all the pellets, wafers, veggies and shrimps provided are devoured down so I guess they are eating
@bcarlos: What you say is also true, not all xantos turn completely gold.. Any tips on how to bring the best out of them?