Wrasse acted like wanted to eat but didnt

My six line wrasse who I have had since June 2014 has been living with a bicolor, a clown fish, and a very very small damsel in a 40g, no problems best friends. First week of Nov added a valentini puffer who seemed to do his own thing never messed with anyone and they ignored him. When feeding came same foods been feeding with no problems since june, some flakes some frozen. All of a sudden in last week and a half wrasse began to get skinny but was just as active came out with everyone when feeding time, but I noticed he would only take a few little pieces and would take chunks into his rock which he never did before. Yesterday he stayed up in rock but would move around to see me, today found him dead on sand bottom. Only difference in last 2 months was new fish and I did a water change with natural ocean water twice. ANY IDEAS?, I could see he wanted to eat, he was just as eager as rest, without the being skinny there was no change to behavior, nothing visible on him