I think one of the reasons that you see negitive threads on wet/dry's is because people are looking for a more natural way to filter. So they take out the bio balls and replace it with liverock and or sand in the sump area to try to accomplish this. There is really no reason to do this. A wet dry is very efficant, bio balls have far more oxygenating capabilities because they have on average more surface area per volume than liverock in its place. More surface area will give you a higher load capacity overall. The other mistake people make is beliveing that a wet/dry with bio balls is a nitrate factory which is only true if you are lazy with maintanance and over feed your tank. If you overfeed your system then any filtration that you have will become a nitrate factory, even a DSB that can't handle the excess nutrients will spill over into the system causing a nitrate spike.
There are opinons out there that wet/dry's should not be used on a reef tank but I disagree, they are easy to maintain, process the water by breaking down the ammonia and nitrites, and provide high gas exchange. Sometimes you may have to clean some of the bio balls which is no big deal, you take out a couple hand fulls and rinse them and put them back, the way some people talk about this chore you would think they had to walk 10 miles down to the sea to get water for a water change.
A wet/dry is just one method of filtration, but they are not as evil as some people think, and like any other piece of equipment you own if properly maintained it will give you good service.
Thomas
