I built one like this... Your gonna want to take that sand out of the middle. The rocks and algae are plenty to cultivate 'pods. The sand will just collect waste like nobody's business. And it is NOT fun taking it out
That is nice. If you are looking for the sand to be a denitrification (sp) you will need a deep sand bed. (at least 5 inches). Are you only keeping corals? The worst thing you can add to a nice coral tank is fish. They really make a lot of waste. Looks like you have a good amout of rock in the main tank. I just sold 200lbs of live rock and all my corals out of my 125 and turned it into a swim tank for my caiman lizard. I loved the corals but Mango has captured my heart.
I wish you the best with your tank. In my opinion the best tank book you can buy is Natural Reef Aquariums: Simplified Approaches to Creating Living Saltwater Microcosms by John Tulock ISBN-13: 9781890087005. This book is worth it's weight in gold.