Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
That is always the place to start: Thorough cleaning, and a bit of petroleum jelly on the moving parts.
Finally filters do die, or you want to upgrade.
Any way to keep the cycled media in the system will keep the biological filtration going while the bacteria move to the new filter media. If the old media fits into the new filter, that is pretty easy. But if the media is wearing out or does not fit, then divide the old media into several nylon stocking or mesh bags, and hang these in the tank. Then remove one bag a week so the bacteria is removed slowly.