I have a 30 gallon tank with two fire-fish gobies and some corals that are still alive and well in the tank. However, recently I tried to add two fish (a blue green chromis and a tribal blenny) and some peppermint shrimp at separate times but the fish die within 3 or 4 days but the shrimp still live and I don't know why the fish are dying. I have tested the water for ammonia, nitrates, nitrites, pH, and salinity and nothing is wrong in that sense. I am afraid to add another fish if they are going to keep dying.