My 2 perc clowns seem to never sleep! i stay up late, usually 1 or 2 am, and they are always still swimming around (lights are off, but you can still kinda see in the tank). in the morning, my wife gets up at 6am or so, and they are swimming. they seem to be very very active... one funny thing that happens is that all the curtains are clsoed in the morning except for one window, and it is not the side the sun comes up on- but a little light gest in. 1st thing in the morning, they swim tilted at a 45 degree angle with their tops towards the window! i have read that fish use light to help balance, and if i turn the lights in the tank on, they straighten right up- turn them off, and within about 30 seconds, they go tilted again! it was really funny when we discovered this- my wife thought they were sick.... but they were just trying to sit up straight!