Check the water quality for ammonia, nitrite, nitrate and pH.
Add some floating plants so it's not as bright for him.
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TURNING LIGHTS ON AND OFF
Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.
In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.
At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.
Try to have the lights on at the same time each day.
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If the fish tank is in a quiet room, either move it into a different room where there is more people moving around it. This can help the fish get use to movement and they stress less when you go in the room.
If you can't do that, then have a television on during the day. You don't need the noise but the light and movement can help the fish get use to things moving around them.
You can use a fan and tie some ribbon to the fan cover. Have the ribbon about 12-18inches long. As the fan blows the ribbon waves about and can help settle the fish. If you have the fan on oscillate, it works better.