Well first off, everything I've read and heard about the wet dry system is you want to stay away from using wet dry/bio balls if you plan on using this sump for a reef setup. Bio balls can, in a wet dry system cause nitrate levels to go haywire after time. Some may disagree but I’ve heard too many negative things about their use so I’m staying away from them. As I said I'm using the model 3 mainly as a means to hold a large protein skimmer in the center and am adding a separate Refugium outside of the sump. I'm using the sump this way because I believe the Refugium setup by Aqueon is flawed. It places your skimmer in the last chamber and will skim out (not all I’m told) the beneficial copepods, amphipods form the Refugium But I look at it this way; if I’ve gone to the effort to set up the Refugium, why on earth would I want to remove ANY of the organisms within it? I know some will say that the critters from the fuge will be ground up in the return pump. I guess that’s unavoidable, but some must make it through back to the tank. Also water flow through the sump is faster, than optimal for a Refugium as well. Lastly, the final chamber of the sump is where water level will rise and fall with evaporation and topping off; not good for efficient skimming with the water level rising and falling constantly. I wrote to Aqueon about this concern, and they have not responded after three queries. Typical. They have my $$ so it seems they could care less. Those are the pros and cons as I see it. Anyone else?