Keep the water quality good, check its not too warm and try to get hold of some live food, I have kept a few species of newts and they all liked live bloodworm, I suppose these are the same thing as in the UK (aquatic midge larva). I once helped with some research into newt breeding sites and spent hours counting newts in ponds, I noticed they often seemed to be eating things that I couldn't see because they were so small, I wasn't very close, so I wonder if even quite large newts wouldnt eat small things like daphnia.