Learn Portuguese (Portugal): Este oceano não é tão profundo como o outro.

While this lesson focuses on the relative superlative ('the most' or 'the least'), this sentence is a great reminder of the comparative of equality: tão + adjective + como ('as ... as'). It is a slightly different way to compare two things!

Can I use quanto instead of como to say 'as deep as'?

Yes! In Portugal, tão profundo como and tão profundo quanto mean exactly the same thing. However, using como is generally more common in everyday conversation.

Why do we use Este and not Esse or Isto here?

Este means 'this' and is used because the ocean is conceptually close to the speaker, and it must match the masculine singular noun oceano. You cannot use isto because isto is only for vague, unnamed things or ideas, and is never placed directly before a noun.

How would I change this sentence to say 'This ocean is the least deep' using the lesson's grammar?

You would change the structure to use the relative superlative: Este oceano é o menos profundo. Notice that you use the masculine definite article o right before menos to mean 'the least'.