My betta is in his 60 litre tank as of Sunday. Previously he was in a tiny 10 litre. He is obsessed with the filter. His old tank had a separate compartment for the filter so this is a new thing for him. The filer has been modified with a plastic bottle and tights to reduce the flow. He is now starting to choose to sleep on top of it. I have other things in his tank he can sleep on. I will include a picture so you can see them. It is pretty scary when he sleeps on the top of the filer. Apart from this, he is active and eating as normal.