Wet dry and bio wheels are now considered basically for principally fish only tanks. Although they perform part of the function of live Rock they have some faults when used with reef tanks where lower nitrate levels are required than with a principally fish only tank. The only good reason to use both live rock and a bio wheel or wet dry is if you have large fish who are messy eaters as using only live rock for messy eaters would take up quite a bit of tank space in a smaller tank where space is precious. However you would need to do regular maintenance on a wet dry or bio wheel to prevent dissolved organic build up followed by dissolved organic shedding and the nitrate rise caused by that. This means manual removal of bio balls and/or bio wheels and cleaning them in marine water and placing them back into filters every couple of weeks depending on fish load. There is no really good reason to use either with a principally coral tank with live rock present unless you have very, very little live rock. Remember this, skimmers remove pollutants. Bio filters such as Wet Dry and bio wheels just convert the pollutants into a more tolerable form of pollutant, or they prepare the pollutants to where they can be recycled within the tank, they do not remove them. The aquarists does this through harvesting macro algae and through water changes. Spend the money on a skimmer.
