How to Make an Overflow Box for a Saltwater Tank

An overflow box, also known as a siphon or prefilter box, is an aquarium accessory that operates as an air pump and filter in the case of power disruption to the primary pump and filter. These boxes are suitable for tanks holding over 40 gallons of water and salt water tanks in which the inhabitants require a constant stream of fresh water for survival.

Things You'll Need

  • Measuring tape
  • Permanent marker
  • 3/16 inch acrylic
  • 1 inch plastic tube
  • 1 inch metal hose clamp
  • 1 inch male PVC adapter
  • 1 inch female PVC adapter
  • 1 inch rubber gasket
  • Cylinder prefilter element
  • 1 inch PVC tubing
  • Heat resistant gloves
  • Circular saw
  • Heat gun
  • Aquarium silicon
  • 120 grit sandpaper
  • Clamp
  • Drill
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Instructions

    • 1

      Measure, mark and cut the following pieces of acrylic: one piece measuring 10 inches by 6 inches; one piece measuring 18 inches by 6 inches; one piece measuring 6 inches by 4 inches; two pieces measuring 10 inches by 4 inches; and one piece measuring 8 inches by 4 inches. These pieces will be the back, front, bottom, sides and divider of your overflow box, respectively.

    • 2

      Sand the edges of all the acrylic pieces with sand paper until smooth.

    • 3

      Put on a pair of heat resistant gloves. Brace the 18-inch piece against a flat, heat resistant edge so that 7 1/2 inches are above the surface of the edge. Hold the bottom piece in a vertical position while slowly heating the top portion with a heat gun. Bend the top piece 90 degrees. Heat the top portion approximately 3 inches higher and fold downward 90 degrees. Hold the bends in position until the acrylic cools completely. This will form the lip, which will hold the box onto the aquarium.

    • 4

      Lay the front, back and sides on a flat surface in front of you with the sides positioned in the first and third position. The 10-inch edges should be in a vertical position. Position the first side at a 90-degree angle to the back. Attach the sides together with a bead of silicon on the front and back. Hold the pieces in place with a clamp and allow the silicon to dry. Remove clamp. Repeat this process, connecting all four pieces together to form a rectangle.

    • 5

      Position the bottom of the box against the bottom of the rectangle. Attach all four edges to the rectangle with silicon. Hold the pieces in place and allow the silicon to dry. Position the divider in the center of your box so that the 8-inch edge is vertical and it bisects the curved front of your box. Attach the divider and allow the silicon to dry.

    • 6

      Remove the protective covering from the acrylic panels.

    • 7

      Position the box in front of you so that the lipped edge is horizontal and closest to you. Drill a 1-inch hole in the bottom of the left side of the box. Slide a male PVC adapter into the bottom of the hole. Slide a gasket over the male adapter in the inside of the box. Slide a female PVC adapter into the top of the hole over the gasket and male adapter. Secure the two adapters together. Seal the edges of the hole with silicon.

    • 8

      Slide a 3-inch piece of PVC on the bottom of the male adapter. Position the sump pump discharge hose against the free end of the 3-inch pipe. Secure the pipe and tube with a hose clamp. Secure the PVC pipe and male adapter together with silicon.

    • 9

      Measure, mark and cut a 16-inch piece of 1-inch plastic tubing. Curve the tubing and attach one end to to the right side of the box 1 inch from the bottom with a dab of silicon. Measure 3 inches from the opposite end and mark the measurement. Attach the tubing to the bottom lip of the box at the measurement with a dab of silicon.

    • 10

      Slide the cylinder prefilter into the top of the female filter and attach the box to the tank.