The reasons why guppies die after turning off the lights at night may be due to the following three reasons:

1. Water quality problems. It may be that there is a problem with the water quality, causing the guppies to suddenly suffer from infectious diseases.

2. It is caused by a cold. It may be that the temperature difference is too large when changing the water, causing the guppy to catch a cold and die.

3. Poor physical condition. It may be that the guppy itself is in poor physical condition, and it will die after a little tossing.

Tip:

Lighting is not a necessary condition for keeping guppies. Try not to shine direct light on guppies, as this will frighten them. If you want to appreciate guppies under lights, you can use diffused light.