Hi, I am new to keeping fish, and have started with goldfish, so will need some good advice. I have bought a 25 litre aquarium, with internal filter and everything seems fine , have treated the water beforehand and my 3 goldfish are happy, so far, so good. The Aquaruim shop I bought it from says that I need to change the water every 3 weeks, is this period also ok to clean the filter?
Also, a silly question
Is it safe to switch the filter off overnight and then leaving in on only during the day?
Does it have to be on overnight. is the electricity it uses negligable?
Thanks.