What am I supposed to do in Sitnalta?

Have you been to the Mer City yet?
There are several hints to help you there.

For one, follow the mermaid into her room.

Then go into the museum and read the plaque.

You will have to find the four seahorses and put them back where they belong.
The location of those horses is covered in the next question.

It might help to map out the area first.  Make note of its size and any
interesting locations.

The scroll you found underwater would be a perfect match for the map, if you
drew a 9x4 grid over it.

You will need to follow the path drawn on the map, exactly as it is shown.

Along the way, you should find four water containers.

Those seahorses just love water.

Now all you have to do is figure out where each one belongs.  Take a look at
the descriptions of the horses.

Notice any relation between the descriptions and the pools of water?

You should.  The seahorses whose description best fits a location should be
placed there.  The next hint will list the proper locations for each horse.

Bird bath (flower garden) -- Sweet-smelling seahorse

Bird nest (in tree) -- Feathery seahorse

Tureen (in statue) -- Soggy seahorse