On friday I added the cleaning crew (15 hermit crabs, and 17 snails) to my new 29g biocube. Saturday all was well but this morning (sun) I woke up to 3 dead snails. Other than my pH being a little low 7.7, everything else looks good. The crabs and the rest of the snails look okay. Is this to be expected or is something going on with my tank.