I have a 75 gallon tank. I have 2 tangs, 3 damsels, 2 clown fish, and a starfish. Every morning i wake up the fish are active without the light on. I then turn the light on and the are active all day and sometimes sleep or whatever. however i work evenings. so the light is off from roughly 5-11. When i get home i turn the light on and the fish are always sitting at the bottom and look as if they are going to die. I then do a water change and everything works out. The next morning they are fine. I have done this about 10 times periodically. and 3 times in the past three nights. I dont know if they are just not active due to the light being off for several hours, but im not sure because the light is off for several hours when i sleep and when i wake up they are active. Some insight would be greatly appreciated