06-05-2010, 07:58 PM
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That's possible. Corys do not like bright light period, so the less light over the tank, just what is sufficient for the plants if you have any, is best. Floating plants help to diffuse overhead light. The CF bulb is better light and produces less heat, so I would keep it, and consider floating plants if you think it is bright.
More likely the issue is the sudden change from dim to light and vice versa. No fish likes that. There should always be light in the room (whether daylight or a lamp or two) when the fish tank light comes on and goes off. This makes a big difference in how the fish react. Having light in the room is closer to the natural dawn and dusk periods that all fish are accustomed to. If you've ever been suddenly awakened at night with bright light, you know what that's like; it's worse for the fish as they can't close their eyes, and it startles them, they panic, and frequently crash into the walls or jump into the lid (or out if no cover). Not good.