no offense but that pet shop is giving you bad advice, in my opinion the secret to a successful fowlr is live rock and a good skimmer. i have a uv cause it came with the tank, it seems to help i guess. also live rock makes it look much more natural, especially when it starts to grow coralline algae. wet drys are nitrate factories for saltwater tanks i guess some people still use them. browse youtube, most of the nice fowlrs have live rock.