Definitely the food. Suns are very tolerant of water conditions but need, basically the same type food you'd feed your fish. I go through a pound of mysid, a bar of Cyclopeeze, a package of Rod's and a bottle of Selcon...plus a mix of others, every month. I have a LOT, though! Pick up a pack of mysid, some Cyclops and a bottle of Selcon or Vita Chem, target feed each head and they'll bounce back in a matter of days