Did you set this on the database-level? If so, then unless otherwise overridden in a query then no you don't need to specify
Setting transaction Isolation Level:
ALTER DATABASE YourDb
SET READ_COMMITTED_SNAPSHOT ON
I'm guessing you did the above?
Also, I hope you understand what exactly this Transaction Isolation Level entails. It has to do with row versioning and is quite the hit on
tempdb. It's not always the answer to heavy "writing/reading". Not to mention it utilizes row versioning, so you may not be getting what you think you should be getting.