Betta fish are tropical fish that originate from Southeast Asia, where they live in shallow, slow-moving waters such as rice paddies and floodplains. These natural environments are not typically lit up at night, so betta fish are adapted to living in darkness.
Providing bright light at night can disrupt a betta fish's sleep cycle and cause stress, which can lead to health problems. It can also make the fish more susceptible to disease and aggression.
If you want to provide your betta fish with a comfortable and healthy environment, it is best to keep the lights off at night. You can use a timer to ensure that the lights turn off at a consistent time each night.