Sorry you've been having bad luck >:[

To be honest, all of the feeder fish I've had have lived for years, it was insane. My sister got a sick W*M feeder because her daughter wanted to save it, and name it Nemo. They first kept him in a small 1 gallon with an undergravel filter and allowed him to grow up a bit before moving him into a 10 gallon, he's over 1 year old now and happy!