Recently bought 4 gold fishes, can i leave the tank light on during every night or off, because may be it affects them?

I have always turned the fish tank light off at night. Fish sleep and have cycles just as we do. Think of the fish in the wild, light during the day, dark at night. Leaving the light on to much will promote allege growth. Good luck with your new fish, take care.

I recommend turning the light off at night. But common/feeder/the cheep  goldfish need about 35-50 gallons of water for 1 fish. And fantail/the fat goldfish need 20-30 gallons of water for 1