How do they clean the aquariums at Seaworld, the Shark is one.

employess must have a conduitinyo another tank that they herd the shark into before entering to clean it in scuba gear.
and probably sucker fish and other organism naturally found eat some debri and do some cleaning like the remora fish who actually clean the shark itself.

They have large filters (usually behind the tanks) that filter the water constantly. They also have large water vacuum cleaners to suck up stuff that is too large for the filters to remove.

There shouldnt be sea worlds the creatures should be free like God intended