Question: how often do you need to change the water in a betta fish tank?
Answer: General Rules of thumb for how often to change a fish tank If you keep your Betta in an unfiltered bowl then you should change 30-50% of the water every week – the smaller the bowl the more water you should change. If your Betta lives in a filtered tank then you only need to change out about 20% of the water each week.