Well, if he swims by the filter and gets pushed around the current is too strong. Male betta especially dislike current because it makes it even harder to swim with already heavy tails, that catch the current.
He may avoid a large area around the filter as well.
There's a good thread on how to baffle a filter on here
He may avoid a large area around the filter as well.
There's a good thread on how to baffle a filter on here
