Gunny reefer, Pompey john is right,,,,,I would have the mechanical filtration, and then the skimmer,after that you would want the refugium,Then the return to your tank...The object to the game is nutrient removal, you run a refugium to filter the water and to make food for the smaller organisms and to stabilize the tank,if you let a bunch of uneaten food or microalgae rot in it ,That is going to led to a bad algae problem,and your skimmer is designed to remove proteins not ammonia...Have a mechanical filter [AKA filter sock] to take out large particles first ,then the skimmers pump is feed the water in that area,Which will make it work more efficiently,the output from the skimmer would go towards the refugium area..From what I can see you would diffintly want to redesign your sump...Just my two cents ,,With over twenty years doing saltwater