perlite ( SP?) mixed into FFOG?

Picked up a big back of that Fox Forrest OCean Grow soil....guy at the store said it had Perlite already mixed in...do i need further perlite? is it absolutly nesseccarry?

Short simple answer YES.
Why? It will drain better, make more oxygen available to the roots, and dry out a little quicker with more perlite. As is, it can take forever to dry out, especially while the plants are young, inviting problems such as root rot, and fungus gnats. You don't HAVE to add more perlite, they can grow fine as is, but its CHEAP, and makes that bag of soil fill up more pots for more plants