Author: zeroinverse So often solutions are given without any reasoning behind it. There are drawbacks to every method, you just have to decide which draw back you want to deal with. Skimmer first: The whole point of a good skimmer is to remove dissolved solids and some solids before they are broke down into base components of nitrates and phosphates. This reduces load on biological filter and removes N and P before they are present. The overflow takes surface water and feeds this dirtiest water to the skimmer.CON: A fuge needs to be fed raw water from the tank for the micro fauna and macro algae to feed off of. The skimmer removes most of this and the fuge gets under fed. Fuge first: Fuge is fed tank water where it feeds the micro fauna and macro algae. Worms and pods feed off the water and break down the waste to base components of N and P. Macro algae takes up the N and P and is removed from the sytem when harvested. CON: The whole point od a fuge is to provide habitat for a strong population of pods to grow with out predation. This populations eggs will eventually overflow and feed the coral and fish in the display tank. With the skimmer after the fuge a lot of the eggs are skimmed out and never make it to the tank. What is the point of having a fuge when you kill most of what it produces? Return last: Regardless of what is first, everything flows through the sump to the return and cycled back to the tank. A fuge is best served by low flow for the pods to grow without holding on for dear life and the time for macro to take up the N and P. The CON is that sump flow is too much for the fuge and you reduce it's effectiveness. Why not have the best fuge you can? Return in the middle: The best of both worlds. Skimmer is fed raw water as is the fuge. The flow is controlled for how much the skimmer processes and how much the fuge requires. Both get what they want. CON: You have to split the drain coming from the tank. This requires probably $10 in extra parts and 30 more minutes at most to plumb. Hard to call that a con when that is all it takes and you get a much better system. Feel free to reduce or improve the effectiveness of your system based on the limits of your individual situation.