could be many things
make sure the light isnt too strong, and that they are being kept between 66 and 74 degrees, i dont think the heater is needed
be sure they r moist enough but do not use tap water
be sure the daylight photoperiod is at least 13 hours
he could've swallowed the coco husk chunks, he could be getting old, or u could be buying from a bad dealer who sells sick, parasitized wild caughts
i breed these guys so if they spawn again do u want me to send u firebelly toad tadpoles or toadlets next year??