Hey everyone, today one of my red mm platys died. I noticed that another one of them is starting to turn white on there head? All the other fish in the tank are perfectly healthy and the water was tested fine. I dont know if that fish is just stressed or what? This has never happened before. I added aquarium salt to the tank about 5 minutes after I noticed and I am hoping that it will do good! Does anybody have any Idea what it could be? Thanks in advance!