DIY Basic Frag Plugs

Today’s post will guide you through the basic steps for frag plugs.

Acroporas on my DIY Frag Plugs

There are just as many ways to make your own frag plugs as there are ways to keep an aquarium.  Experiment, and find out what works best for you!  In my opinion, this was a good basic way to start with equipment you should have lying around your home or can purchase locally and inexpensively.  Since starting with this basis I’ve just about perfected my version of the DIY frag plug using additional equipment.  The ratio of concrete-to-sand will determine the aesthetic appeal as well as the breakability of the frag plug.  A frag plug needs to be sturdy enough to hold up in an aquarium yet fragile enough to break with a small amount of force.

There is debate over using cement in an aquarium…how long it must cure…etc.  I’ve made these for years, and I’ve had hundreds of these in my aquarium.  I can’t guarantee what works for me will work for you, but I have had no ill effects.

Supplies Needed (minimally):

1 cup Portland Type 1 Cement 
2 cups fine sand (Home Improvement Store Play Sand works fine for the mould, but you’ll need 1 cup of nice sand)
1 cup Aragonite, crushed shells, etc.
RO/DI water
Frag Plug template
Shallow pan (I use a Rubbermaid tub lid)
Dust mask
Safety goggles
Old toothbrush
Disposable mixing container and utensils


Step 1:  Gather all necessary supplies

Step 2:  Read all directions, manufacturer’s labeling, and safety precautions.

Step 3:  Wear all safety gear.  Concrete dust is very harmful to skin and eyes.

Step 4:  Fill the pan with fine sand.  Any flat, durable surface that can be filled a few inches deep with sand will work.

Step 5:  Wet the sand, but only until it is able to be formed.  Do not make sand soup!

Step 6:  Level the sand with a flat straight edge, like a ruler or a piece of scrap wood.

Step 7:  Make your mold tool.  I tried several different items, including old frag plugs (which I consider cheating…and they don’t work well), the bottom of a shaving cream can (one of my favorite moulds…no joke), a milk jug lid, an acorn top (hehe…this made a fun frag plug), a pen cap, an Elmer’s Glue cap, etc.  The best basic frag plug design ended up being the acorn cap with the peg formed by a pen cap.  Go figure.  The bottom of a shaving cream can was useful to create concave disks to hold corals that might float away.  The bottom of a soda can works equally as well.

Step 8:  Use your mould tool to make holes in the sand.  Leave a few inches between mould holes.

Step 9:  Double-check your moulds for cracks, uneven sand, etc.

Step 10:  Add 1 part (1 cup) Portland Type 1 Cement to the disposable container.  Add two parts (2 cups) fine sand and one part (1 cup) aragonite/crushed shells/etc.  The larger sands/shells adds texture and creates a more conducive surface for a coral to grow on.  Stir the mixture together, being careful not to breathe the dust.  Add enough RO/DI water to make a soupy mixture.
Step 11:  Pour the cement mixture carefully into the moulds.
Step 12:  Using an old toothbrush, lightly brush the top of the plugs to give a rough surface on which to apply glue/epoxy when cured.
Step 13:  Let the plugs sit in the sand for a few days (at least one, weather dependant) for the cement to set.
Step 14:  Pull the plugs gently out of the sand when the cement has set.

Step 15:  Allow the plugs to dry in open air for about a week.

Step 16:  Place the plugs in RO/DI water with a powerhead to cure.

Step 17:  Change the RO/DI water every few days.  This allows the plugs to leach whatever they leach safely, outside the aquarium.

Step 18:  When the water’s pH tests between 7.6 and 8.4, change the water to old aquarium water from a water change if possible.  Use saltwater if old aquarium water is not available.  Add a heater and heat the saltwater up to normal reef temperatures.  I usually add a tiny bit of live rock as well.

Step 19:  After about 4-6 weeks, the plugs should be fully cured.  Although the cement itself has fully cured, the plugs may still cause an algae bloom due to additional leaching.

Montipora on my DIY Frag Disk (made from a coke can)
Acanthastrea on my DIY Frag Disk (made from a milk lid)
Tips and Tricks:

1.  Do not use the concrete mixes.  Although they may look neat for DIY live rock, they are not the right consistency in my experience for frag plugs.

2.  If you can find it, Portland Cement also comes in white instead of gray.  There are also concrete dyes available if you want your plugs to have a “coralline” color to them.  I am not aware of the reef-safeness of the dyes, so use with caution.

3.  Rock salt may be added to the concrete mixture after adding the RO/DI water.  During curing, the salt will dissolve out of the rock and leave the plugs more porous.  Rock-salted plug cure time may be sped up by boiling the plugs to remove the salt faster.  Keep in mind, if too much salt is added, the plugs may look deformed by all the holes.

4.  Plastic shavings, shells, rock salt, and other interesting objects may be used in substitution of the calcium based aragonite for texture.

5.  To help prevent an algae bloom when adding the cured plugs to the tank, keep them in a low light area for one to two weeks.

6.  If your toliet has never had the blue toliet disks or other cleaning agents in the back, you may place the frag plugs in a mesh bag in the back of the toliet (and if your significant other approves!)  Each flush of the toliet is a water change!

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