I recently expanded my CUC with dwarf ceriths, a few more star astreas, and 3 scarlet hermit crabs. The tank has no fish, ammonia reads 0 (seachem gas exchange sensors), nitrates at 10, phosphates 0.03, Alk 10, Ca 450, Mg 1350, all salifert. There were already two ceriths and two star astreas in the tank. The snails are doing well and chowing down but the hermits have all died after 2 days. They were actively exploring and grazing on days 0 and 1, but today I found them half hanging out of their shells and nonresponsive. What could be wrong with my water? Temp has been stable at 78 and pH is currently 8.2 with 35.2 ppt salinity. Salinity has been very stable but I don't check pH regularly.