Do it yourself PVC Aquarium Cave

by Mark and Esther

Step by step instructions for building an attractive aquarium cave using a PVC pipe, aquarium gravel, and silicone.

Materials Required    
(in Canadian Dollars)
4" PVC Pipe Y Whatever size you want your cave to be, but don't use ABS, copper, or steel pipes, as they can contain chemicals that are not healthy for your fish.
$ 5.96
Sandpaper Something very coarse, like 60 grit. However, any sandpaper will work if you have some handy.
$ 2.68
Aquarium Safe Silicone
We used GE Windows & Door 100% Pure Silicone Rubber. Make sure that the silicone you choose does not have any mildew resistance, or it will harm your fish.
$ 4.78
Aquarium Gravel or Sand Use some from your aquarium if you want the cave to blend in.
  Misc An old towel, some newspaper, some cardboard pieces  
Total Cost: The total cost could be reduced to $10.74 if you already have sandpaper.
$ 13.42
Tools Required  
  Safety Glasses

Dremel / Jigsaw / Hacksaw

Rubber gloves (if you don't want to get messy)
Sharpie Marker

Fan (optional)

  Hair Dryer (optional)

Supplies we picked up at the local hardware store.

Step 1:

Decide how tall you want your cave to be, and leave a little bit of extra room for the gravel on the floor of the aquarium. Mark the PVC pipe along the lines where you wish to cut. Don't worry too much about getting it straight, since it isn't going to be sitting on a perfectly flat surface anyways.

Mark the pipe where you want to cut it

Leave a bit of space for where the tunnel goes into the gravel

Step 2:

Put your safety glasses on. Using a hacksaw, jigsaw, or dremel with a cutting wheel, cut along the lines that you have made. I used a dremel because it is much easier to handle, and very quick. If you are using a dremel, take your time. Go over the cut lines a few times, making the cut deeper and deeper each time. This will make the next step easier, as you will get fewer burrs on the edges.

Cut the pipe

Notice the rough edges.

Step 3:

Using the dremel with a grinding attachment, (or sandpaper, but it will take longer), grind off the burrs from the cut edges, and smooth the edges so they are not sharp. Make sure you make all the corners nice and smooth, so that your fish won't hurt themselves.

Grind the edges of the pipe until they are smooth.

Step 4:

Sand the outside of the the sandpaper The silicone will stick better if the surface of the pipe isn't smooth and shiny. Rinse the pipe under the tap after sanding and grinding it to get all the dust off. Using the silicone, put a few dabs on the pipe in random areas to make sure it sticks. If it sticks well to the pipe after 30 minutes, you should be fine. If not, you may need to sand more, or to get a different type of silicone.

Sand the pipe to make the silicone stick better.

The pipe, smooth and ready to go.

Step 5:

Get enough gravel to cover the surface of the pipe, We took some out of our tank, since we wanted the cave to blend in. Since the gravel was all wet, we had to dry it. Grab an old towel, and spread the gravel out on it. Using a hair dryer, blow on the gravel while mixing it with your hands. This method seemed to be very quick and only took about 10 - 15 minutes.

Use a blow dryer to dry the gravel quickly.

Step 6:

Spread some newspaper on the working area, and move the gravel from the towel onto the newspaper.

The pipe and gravel, ready for next step.

Step 7:

Liberally apply silicone to one area of the pipe at a time. Smooth it out over the surface with a piece of cardboard, or your finger (wear gloves if you don't want to get messy). Once you have applied it to one area, roll the pipe in the gravel or sprinke the gravel over the pipe. We did both, the rolling seemed to work ok for the first one, but we sprinkled after that.

Do one section of the pipe at a time and allow the pipe to dry for about half an hour between sections.

After letting each section dry, lightly brush your hand over the gravel to get rid of loose stones. Also, pick up the pipe and shake it lightly. This will reveal some bare spots which you can touch up by putting a dab of silicone on the empty area, then sprinkling gravel on it, and lightly pressing the gravel into the silicone.. Repeat this step until you are satisfied with the look.

Flip the pipe upside down and put some silicone and gravel on the inside near the openings to make it blend into the scenery a little bit more.

Cover the lips of the pipe last, when everything else is dry. Put a nice thick bead of silicone all the way along it, then squish it down onto the lip. Press some gravel into the silicone until you can't see the lip anymore.

Once you are happy with the look of your cave, let it sit for at least 24 hours to let the silicone fully cure.

Spread on the silicone

Roll the pipe in gravel

Sprinkle more gravel on

Push the gravel into the silicone

Let the top and sides dry

Apply silicone and gravel to inner pipe

Push the gravel into the silicone to make sure it sticks

Put a thick bead of silicone on the lip and push the gravel in.

Allow each section to dry for at least 1/2 hour before moving to next section.
When fully covered, give it at least 24 hours for the silicone to fully cure.

Step 8

Now that the silicone has dried nicely, give it a final light shake to remove any loose gravel.

Carefully rinse the cave under the tap, and then submerge it into a sink or bucket of water. Let it sit for 24 hours, then dump all the water out. Repeat this for at least 3 days to clean it well before introducing into the aquarium. We used some water conditioner in the water on the last day to make sure there was not any harmful chemicals present.


Rinse the Cave

Let it soak for a few days

Step 9

Place your finished cave in your aquarium and watch your fish enjoy their new toy! Give yourself a pat on the back, and take some pictures of it to share with us!

Finished product, installed

Our Tiger Barbs enjoying their new hideout


"I just want to say thank you for your great idea on making caves.They look great and are easy to build.I like the looks of these better that the ones the LFS carry.I am going to start making a few tonite. - Thank you, Mike"
"My new cave looks great in the aquarium. Thanks for the tutorial!" - Jim Nebbins, Montana

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