Have you ever watched your fish just dart off in hurry then make a sudden stop only to repeat the darting action a few seconds to minutes later?.
Typically when this happens it is usually a case of high alkalinity in your tank. When your alkalinity or KH is to high it will usually cause darting, fin rot, popeye, and may lead to death.
Most Salt water fishes need a kh of 8 to 12. Alkalinity test here. Adding too much baking soda to your aquarium will significantly raise the alkalinity.