i had mine in my hospital for 1-2 weeks about 2 months after i got him, i saw he was getting really thin was thin when i got him also , anyway it was just plain tank ( this is obcourse before i knew about them only eating copods, anyway i just put in some frozen brine and eventually he started eating it, i actually just bought one yesterday i made sure it was eating frozen before i said i was taken him, also made store put on hold till sat this way i can once again make sure he is still eating frozen