Fish Sleeping Habbits

[Gauge]

I don't really know anything about the sleeping habbits of fish in general. My chromis and clownfish all seem to find some sort of hiding spot and just swim in place for the night. They lose their color and stop reacting to stimuli until the lights are turned on (generally). However, I want to know how to tell that there are issues at night with sleeping fish. My longhorn cowfish, for example, swims around at the surface of the water pretty much all night and doesn't seem to find a spot and stop moving.

1) Is that a normal sleeping habbit for a boxfish?
2) Do fish sleeping habbits vary much? If so, what are some examples?
3) How can you tell your fish are having trouble with their sleep time?

 

[Munskins]

Boxfish, correct me if im wrong, are most active at night and sleep in the morning.

For some odd reason my huma picasso and my blue tang always sleep around 11:00 even if the light isn't off. Maybe its because their old?