I've got a 20" Green Serpent Star and just recently he has been eating less and the tips of his tentacles have been looking withered. Just today i found a 1" piece of one of his tentacles has broken off. Is he sick or, maybe molting?

My parameters are:

Ammonia - 0
Nitrite - 0
Nitrate - 0
Phosphate - 0
Salinity - 1.026
PH - 8.4
Alk - 10
Ca - 420
Mg - 1320
Tom