As described in Slugkeeping FAQ, one excellent way of having a box of slugs is to set it up as a refugium (a fish-free zone that allows proliferation of plants and small organisms) in line with a marine aquarium.  The plants can make use of the nutrients (phosphate and nitrate) produced by the fish and food, reducing their concentrations in the display aquarium while providing food plants for the slugs.  Further, supplementation of calcium and carbonate for corals will also support growth of calcareous algae, such as Halimeda or Penicillus.  The only concern is avoiding pumps or strainers that the slugs will inevitably encounter and be killed.

A 27 gallon cube (20″ wide X 18″ deep X 20″ tall) was a good fit for the available space, and I found a used stand that fit with the decor reasonable well.  To accommodate input from the coral reef tank, and overflow back to the sump, I drilled a couple of holes in the back, and added bulkheads plus fittings.Because the flow through the tank will be very low, there is no need for fancy overflow systems.

Holes for connection to reef tank.

Input from reef tank (left), drain to sump (right)

Then it was just a matter of adding sand for the plants.  For a little topography, I added a large-ish piece of base rock.  In case flow from the main tank circulation fails, there is also a Hydor heater/pump combination to act as a backup.  It has a sponge attachment for the intake that ensures slug safety.

Box of Slugs 2.0

Nice thing about adding a tank to an established system is that it is ready for inhabitants.  KP Aquatics (formerly SeaLife Inc) sent me a nice batch of macroalgae, and I indulged myself in a few photosynthetic gorgonians as well.  The Elysia clarki settled in well.

Box of Slugs 2.0 with macroalgae and gorgonians