Hello, I've had this 88litre tank set up since the end of June and putted cycled media in the filter. It's been a few weeks since I've seen my fish swimming sometimes floating in the middle of the tank in front of the filter where the water gets sucked up. I know the filter isn't sucking my fish in because he's only acting like this now. My fish only swims around normally to eat its food or if he gets disturbed but he will just keep going back to the middle of the tank after. I clean about 10-20litres of water every week, sometimes a few days but I've never been past 2 weeks without a water change. After every water change I add aquarium salt too. Also my fishes dorsal fin seems to always fall on its side and is hardly erect. Btw my goldfish is an Oranda and I've had it for 2 years. What should I do to make my fish act back to normal?