A cucumber is great to maintain the tank of excess detritis but you still need to syphon out the existing detritis for fear of escalating phosphate levels... that will lead to an algae bloom...
Get a Brittle Star and a Fighting Conch.....and/or maybe a Sand Sifting Star. Thats what I have in my tank.well not the Sand Sifter yet but thats next. Got a Spiny Star today.