You might want to reconsider on putting a wet dry system on a reef. They are prone to drive nitrates up in a tank. They are good for fish only tanks where nitrates are not so much a concern, however, on a reef nitrates need to be maintained near 0ppm.
A good option might be a 20l tank made into a sump with multiple compartments to hold a refugium, a skimmer, and a return pump.