What kind of filter do i need for a 55 gallon reef tank?

i just bought a 55 gallon saltwater tank off of some guy he had it set up as a reef tank with lots of live rock and coral. he had a whisper filter hanging off the back and that is it for the filtration is that enough or do i need to upgrade. different pet stores tell me different things one said i need a wet/ dry system one said i would be fine with a canister filter im just confused all around with the research i have done online.