I have a 24g nano but cannot keep fish alive. My ammonia is 0 nitrites and nitrates are 0 salt is @ 1.025 14lbs live rock 25lbs live sand 14 crabs 8 various snails a diamond goby and 1 skunk shrimp all doing well but have had 3 dwarf angels 1 clown 1 bangi cardnal all die not all in the tank at once of course. Can you tell me why?