Hi, I have a male betta in a 25 litre aquarium, at the moment I have a sponge filter in his tank, just wondered can anybody recommend an internal filter what won't be to strong for him or tear his fins.
the TOM internal filter is very cheap, and has a spray bar attachment which really mutes the flow. It pretty much is just a sponge and a small chamber which you can fill with either carbon or some pieces of ceramic, but mine is still going strong and i think i payed like $11. Oh an its small, some of those internal filters are so huge now!!
The Interpet PF works fine for bettas in my experience.
They are easy to clean and you can change the power and direction of the flow as you wish. For a 25 litre I would recommend the Interpet PF Mini