How to Make a Deep Sand Refugium

A Deep Sand Bed (DSB) refugium, also known as a remote DSB, provides many substantial benefits for reef tanks. As aragonite sand dissolves, it provides free calcium for corals, and helps maintain alkalinity. Any DSB helps keep nitrate levels near zero. The remote DSB also provides a site for macroalgae growth and harvest. Additionally, a remote DSB offers a predator-free habitat for copepods and other marine microinvertebrates.

Things You'll Need

  • Refugium
  • 2 bulkheads, 1 inch
  • Drill
  • RO/DI water
  • Aragonite sand
  • Reef tank light
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Instructions

    • 1

      Choose a vessel to house the remote DSB. This decision involves two factors: budget and vessel depth. A five-gallon bucket is a simple and cheap solution, and will create a perfectly acceptable and functional DSB. Aquarists can also choose from any number of custom-designed refugiums or refugium-integrated sumps at a substantially higher cost. Square containers will be easier to work with in either case. The vessel depth must allow for a sand bed depth of at least six inches, and up to a foot if possible. A sand bed of less than six inches lacks the anaerobic capacity to complete denitrification. Choose wisely.

    • 2

      Install the two bulkheads to allow for one to two inches of clearance between the top of the eventual sand bed and the bottom of the bulkhead. The drill will be needed for the holes. Bulkhead placement must facilitate adequate water movement over the entire surface of the sand; placing the bulkheads in a linear fashion will cause linear water movement, so offset the bulkheads to make the water swirl around. Think about what would happen if the power went out and plan for this eventuality; the power always goes out at some point. Create a siphon break or leave enough room above the bulkheads to accommodate extra water.

      Note: If the DSB is located in a pre-fabricated sump, no bulkhead installation is necessary. Skip to Step 4 and fill the designated area with sand to the desired depth.

    • 3

      Place the remote DSB within the overall tank system. Placement should be done in a way that ensures passive water flow over the DSB. This means no pump or powerhead should be needed to expedite the flow of water away from the DSB vessel. If the DSB is in a standalone vessel, it should be upstream from the sump. If the DSB is incorporated into a larger single-unit sump, the DSB should be as far upstream from the return pump as possible. This minimizes the chance of a catastrophic clog in the outflow line and will preserve a higher proportion of microinvertebrates as they journey back to the display tank.

    • 4

      Test the bulkhead installation by filling the container with RO/DI water. Cap the bulkheads or install tubes that can be extended above the waterline during the test, otherwise as water reaches the bulkheads it will simply run out and spill on the floor. Once the bulkheads are deemed watertight, drain the RO/DI water back out and fill the DSB container with aragonite sand to the desired depth.

    • 5

      Choose the final resting spot for the remote DSB. Once chosen, connect the bulkheads to the rest of the system.

    • 6

      Install a reef tank grade light over or near the DSB if a goal is to keep macroalgae or microinvertebrates for harvest. The light doesn't have to be high-end; a simple 55W PowerCompact (PC) fluorescent will do. Just don't try to use an incandescent or greenhouse light.