First it was my panda cory. It was fine one day and the I noticed it did not eat and less than 24 hours later it was dead. The same exact thing has happened to another cory, a cardinal tetra, and now my number one fish, the male blue ram. He is still alive but I fear the worse. I checked the water parameters and everything is ok ammonia, nitrite, nitrates. They just stop eating, sit in the corner and then die. I already did a large water change, what should I do, what can I do!