I still think that he is starving. Basically, from what I have heard, they basically hunt, and eat about 20 hrs a day. So even feeding 2-3x a day is not enough. Also just read another thread where a guy works with mandarins a lot, and one species has a MUCH higher success rate than the other. The other one you had, was it a different species than the one you have currently?
When you say tails disappearing, I automatically think fin-rot. Also, if the fins are rotting, that flesh is dead, and COULD be why the snails are most-likely eating it.