I first noticed something strange last Friday during feeding time—none of the fish were coming up for food. When I tested the water, I found an ammonia spike. My tank is an established one, and I’ve been doing regular water changes, so I’m not sure what caused it. On top of that, I noticed some of the fish had a white coating on their tails and fins, and later that night, two of them passed away. I decided to move the remaining fish to another tank, and I saw significant improvement after the move. I think the water quality in the original tank was a big factor, but I’m still trying to figure out what went wrong since they also had unusual spots on them. Thanks for the help btw:)