DIY: HOB Overflow

A sump sits below the main aquarium and is connected to it via both a pipe from the overflow box. A submersible pump in the sump returns the water to the main aquarium. Sumps increase the volume of water in the system and offer a remote area in which to hide heaters and filters. Aquariums that do not have pre-drilled holes and cannot accept piping require a hang on the back (HOB) overflow box to channel water down to the sump. Aquarists can design and build their own hang-on-the-back overflow boxes.

Things You'll Need

  • Aquarium, 36-inches long and 12-inches wide
  • Glass box without top, 5-inches long by 2-inches wide by 5-inches deep, with pre-drilled, 1-inch diameter hole in the bottom
  • Work surface
  • Two plastic brackets
  • Tube of non-toxic, 100 percent silicone sealer
  • One, 1-inch bulkhead
  • One, 3-inch long, 11/4-inch diameter piece of PVC pipe
  • One, 16-inch long, 1-inch diameter piece of PVC pipe
  • Sump
  • Glass box, without top, 4-inches long by 2-inches wide by 5-inches deep
  • Two plastic brackets
  • U-shaped, 1-inch diameter pipe, 8-inches long
  • Aquarium pump, rated at 300-gallons per hour
  • 2-foot long tubing
  • Plastic clamp
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Instructions

    • 1

      Lay the glass box with pre-drilled hole on a clean and dust-free work surface and glue two plastic brackets onto the box, so that it will hang over the back rim, on the outside of the aquarium. Use 100 percent silicone sealer and leave the sealer to cure for 24 hours.

    • 2

      Lay the second glass box on a clean and dust-free work surface and glue two plastic brackets onto this box, so that it will hang on the back rim, on the inside of the aquarium. Use brackets long enough that the top of the box is slightly higher than the water level in the aquarium. Use 100 percent silicone sealer and leave the sealer to cure for 24 hours.

    • 3

      Place the bulkhead in the predrilled hole in the base of the first glass box so the threaded end points into the box. Push the bulkhead gasket onto the threaded end. Screw on the bulkhead nut and tighten. Spread a teaspoon of non-toxic, 100 percent silicone sealer around the bulkhead on the outside of the box to ensure a water tight fit.

    • 4

      Push a 3-inch long piece of PVC pipe over the threaded end of the bulkhead.

    • 5

      Hang the glass box over the back rim of the aquarium, on the outside.

    • 6

      Push one end of the 16-inch, 1-inch diameter PVC pipe into the bulkhead, from below. Spread a teaspoon of non-toxic, 100 percent silicone sealer around the join to ensure a water-tight joint.

    • 7

      Place your sump directly below this 16-inch long pipe, so water flowing from the pipe will pour into the sump.

    • 8

      Attach the 2-foot long piece of tubing to the pump and place the pump into the sump. Place the opposite end of the tube into the aquarium. Secure it onto the rim of the aquarium with a plastic clamp.

    • 9

      Hang the second glass box over the rim of the aquarium, on the inside. Hang it directly opposite the box on the outside.

    • 10

      Fill both glass boxes with aquarium water.

    • 11

      Hold the u-shaped tube underwater in the aquarium, so that it fills with water. Place a thumb over each end, underwater, and lift it out, ensuring the water remains inside. Place one end into each of the boxes. Place the ends underwater before releasing your thumbs.

    • 12

      Turn on the sump pump. As water from the sump enters the aquarium, the water level will rise until it flows into the box in the aquarium. Water will flow through the u-shaped tube into the outside box and from the box, back to the sump.