Everything is already said. Anyway, here are my options:
- no hace falta decir que...
- está de más decir que...
- no hay ni que decirlo...
And I would like to point out
:- huelga decir sounds to me formal and old fashioned.
- If you use implícito it goes with estar: está implícito en el contexto...
- I would say that obvio and implícito have different meanings, but you can also think how you use their literal translations in English and decide if they are synonyms or not.