a lot of established live rock, (1.25 to 2 lbs per gallon), serves the same purpose as a wet/dry filter: biological filtration. if you've got a heavy bio-load, (lots of fish or messy eaters), a wet/dry filter definetly wouldn't hurt, especially in conjunction with a protein skimmer. the skimmer will remove a lot of the doc's, (dissolved organic compounds), from the water before the wet/dry has a chance to convert them. a fuge serves a different purpose, your plantlife will remove things such as nitrates from the water, and if you use a dsb in your fuge this will also help to complete the nitrogen process. wet/dry's convert ammonia to nitrite to nitrate. HTH