Hello, I've always had platies in my aquarium ever since I began my aquarium hobby a few years ago. Every once in a while, a platy (or two) gets really skinny and sickly looking. Their heads all of a sudden get slanted downward like the one pictured in the post and then a week or two later they die. What's causing this? Has anyone else had these problems? My water parameters are normal, and I do regular water changes. Why does this keep happening and how can I stop it?