$5 DIY Magnetic Coral Frag Plug (mag-frag) for Reef Aquarium




Here is a simple and inexpensive way to make a magnetic frag plug to attach corals to the glass or acrylic sides of your tank. I spent about $5-7 total in materials and that's enough to make a few of these.

Materials & Tools:

  • Large frag plug or simply a piece of rock big enough to carve into
  • Some cheap craft magnets - I got mine at Harbor Freight
  • Some plastic milk jug caps. If possible get one slightly smaller so it will fit inside the bigger one
  • A hammer & chisel or screwdriver to cut the magnet. A hacksaw or Dremel cutoff wheel is useful to start a score line
  • Various adhesives including Quick setting 2 part epoxy, superglue, and hot melt glue
  • Dremel with a coarse grinding stone (Dremel 83142 silicone carbide Grinding Stone)
  • A piece of rubber or something to create friction on the outside of the glass. I used a piece of shower liner but you could use a chunk of mousepad, or a jar lid gripper. Something so that the mount doesn't slide down the glass.
  • Gloves, safety glasses, & a dust mask

Cut the magnet & modify the frag plug/rock

  1. Use a hack saw or a cutoff wheel on a Dremel to make a shallow cut where you want the magnet to break. Then use a chisel or a sturdy screwdriver and give it a good whack on that line to split the magnet into 2 pieces. I made one side smaller so it could fit into the frag plug easier. Wear safety glasses for this. Clean off the magnetic dust with a damp towel.
  2. Use the Dremel to carve out an area inside the frag plug or rock for the magnet. Wear a dust mask and safety glasses. I used a coarse grid grinding stone with a slow speed.


  1. Clean off the frag plug and magnets. Plug any holes with some putty of some sort so the epoxy doesn't leak out. Pro tip - pack some of the powder from grinding into any large holes and then apply a drop or 2 of superglue (the thin kind not gel) and it will harden almost instantly into a permanent plug. Can use baking soda as well.
  2. Mark the polarity of the magnets (so you know which sides need to face each other to stick!).
  3. Mix up the epoxy per the instructions. Usually it's just 50/50 parts A & B. Mix it thoroughly!
  4. Put some epoxy into the carved out hole and then lightly press the magnet in - you want a layer of epoxy under the magnet. Add more epoxy so that it's overflowing from the hole and completely encapsulates the magnet.
  5. Empty the remaining epoxy into a milk cap and embed the other side of the magnet, making sure you're using the correct polarity. Let the epoxy set up.
  6. Use hot glue and glue the larger milk cap over the smaller one, fully encapsulating the magnet so if it accidentally gets wet the magnet won't rust.

  7. Cut the rubber piece into a circle and use superglue to attach it to the milk cap that will be against the glass (in my case I used the larger milk cap as the side that sits against the glass).

Disclaimers & other notes

  • Wear safety glasses & gloves. Also wear a dust mask while grinding or do it outside.
  • Make sure that all the glue/epoxy has fully cured before adding it to your aquarium.
  • I have not tested the longevity of the design or it's materials. You should choose an epoxy that you believe will hold up to the environment you plan on using this in. Many items we use in our tanks are encapsulated in epoxy so this isn't a new concept.
  • For added grip a piece of rubber could also be glued onto the back of the frag plug so it grips the glass better. I felt that the grip was fine as I had it though.
  • For a more professional look you could paint the outside assembly black or some other color.
  • I used large, cheap magnets. You could also do this with smaller or more powerful magnets. Don't go so strong that you put too much pressure on the aquarium glass though or it could break.
  • You don't have to use a large frag plug or rock. You could use a standard round ceramic plug and epoxy the magnet on it's exterior.

Happy Reefing!



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