I had a royal gramma and a porcelain crab for about 2 weeks and just found them dead. I have a 29 gallon biocube. I also have a blood shrimp, hermit crab, a snail and a bunch of blue hermit crabs that are just fine. Checked the water and everything seems fine. The only thing is my ph is a little off at 7.8-8.0 and nitrates at 40. Any ideas??