How to Build a Calfo Overflow Box for a Reef Tank

The Calfo overflow box moves water from the display aquarium to the sump. The sump is a container or reservoir that stands beneath the aquarium and is connected to it via inflow and return pipes and tubes. According to Anthony Calfo, an aquarium specialist, organic material in the tank bonds to surface water, and the sheet of water that travels over the overflow weir carries these organics with it. The Calfo overflow box is longer than other designs and is designed to allow a thinner amount of water to flow from the aquarium. A Calfo box can be constructed by the hobbyist. (See Reference 1)

Things You'll Need

  • Aquarium, 24 inches long and 12 inches wide (with back glass pane predrilled and a 1.5-inch hole just below the water level)
  • One 1-inch bulkhead
  • 1.5-inch PVC fitting, adapted to the 1-inch bulkhead
  • One sanitary-tee, topped with a threaded adapter and a screw-on cap
  • One true union ball valve
  • One 3-inch long, 1-inch diameter piece of PVC pipe
  • One 16-inch long, 1-inch diameter piece of PVC pipe
  • Glass box without back pane or top, 20 inches long by 2 inches wide by 2.5 inches deep
  • Tube of non-toxic, 100 percent silicone sealer
  • Roll of masking tape
  • An assistant
  • Work surface
  • Aquarium sump
  • One return pump, rated at 300 gallons per hour
  • 2-foot return pump tubing
  • Plastic clamp
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Instructions

    • 1

      Position the bulkhead in the predrilled hole in the aquarium's back panel so that the threaded end points out of the aquarium. The bulkhead gasket will be on the inside of the aquarium.

    • 2

      Attach a 90 degree angle elbow to the bulkhead fitting, inside the aquarium. Position the elbow so that it points upward toward the ceiling. Monitor this elbow once the system is working, to ensure that it does not clog, or the aquarium will overflow.

    • 3

      Lay the 4-sided glass box on a clean and dust-free work surface, with the front pane flush with the work surface.

    • 4

      Run a continuous bead of non-toxic, 100 percent silicone sealer along the thin edges of both side panes and along the side of the bottom pane.

    • 5

      Position the glass box, silicone side towards the aquarium back panel, against the back panel. Position the box so that the predrilled hole and the bulkhead fitting and elbow lies within the box and so that the top edges of the box will be just below where your water surface will be. The distance that the glass box is placed below the water surface is very important.

    • 6

      Request that the assistant hold the glass box firmly in place, and using twelve strips of masking tape, secure the box to the aquarium. Leave the silicone to cure for at least 24 hours.

    • 7

      Attach the sanitary-tee to the threaded end of the bulkhead, on the outside of the aquarium. Make sure that the join is tight. Spread a teaspoon of non-toxic, 100 percent silicone sealer around the outer join, to ensure that the join is water tight.

    • 8

      Push a 3-inch long piece of PVC pipe with a 1-inch diameter into the bottom of the sanitary-tee. Make sure that the join is tight. Spread a teaspoon of the silicone sealer around the outer join, to ensure that the join is water tight.

    • 9

      Push the free end of the 3-inch long PVC pipe into one end of the true union ball valve. Make sure that the join is tight. Spread a teaspoon of the silicone sealer around the outer join, to ensure that the join is water tight.

    • 10

      Push one end of the 16-inch long, 1-inch diameter PVC pipe into the other end of the true union ball valve. Make sure that the join is tight. Spread a teaspoon of the silicone sealer around the outer join, to ensure that the join is water tight.

    • 11

      Position the sump directly below the 16-inch long, 1-inch diameter PVC pipe, so that water flowing out of this pipe will flow into the sump.

    • 12

      Position the return pump in the sump and attach the 2-foot long piece of tubing to the exhaust nozzle of the return pump. Place the free end of the tube into the aquarium. Secure it on the aquarium rim with a plastic clamp.

    • 13

      Remove the masking tape from the glass box.

    • 14

      Fill the aquarium with water. Allow the water to flow into the Calfo overflow box and down into the sump, until the sump is 70 percent full.

    • 15

      Plug the return pump into a wall power source and switch on.