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
Depending on the size of the heater,you can have that in either the chamber near the water coming in the sump,or the area where the water leaves,,anywhere there is a high flow...what type of skimmer are you using...you would want the water to be filtered before it goes to the reactor,or it is going to jam or clog up because of debrie .and if any thing that decomposes is left in their,you would actually be hurting the system rather than helping,,I don`t understand why people feel the need to have such high partitions on their sumps,It just makes it harder to work on them....It would only serve a purpose if a skimmer had to have a certain depth to operate effectively..other than that it is wasted space and time
One Thing I Would Say, Depending On Return Pump Size. A 1" Bubble Trap Section Cut Into Two May Allow Micro bubbles From The Skimmer To Get Sucked Into The Tank. Because The Water Will Flow Fast Through it. I Would Make The Incoming Water Section As Small As Possible.