Is there a pronoun for aquarium?

The pronoun to take the place of the noun aquarium is it. Example:

The aquarium is new. It can be a lot of work but it can also be relaxing.

The pronouns to take the place of the plural noun, aquariums, are they as a subject, and them as an object. Example:

I find aquariums interesting. They have such a variety and you can stock them with so many different kinds of creatures.