The Premier Pet Fish Wesite - Established 1996

PVC Cave Towers

By Tam-Tam

With rock substrate
I came up with this version of PVC Pipe caves when I was trying to figure out a way to have natural looking caves for African Cichlids (Mbuna species), without having the added weight and stress of heavy rocks in my fifty five gallon tank. From my research I learned that these rock dwelling fish may only swim as high as the rocks are placed in the tank. So I decided to stack the caves on top of each other in a secure fashion that allowed each fish a place to feel safe. This reduced the weight and I could make the towers as tall as the water level in the tank. I soon realized that this could be very versatile in the tank and allowed for a larger swimming area.

With sand substrate
I feel these caves can be used in any tropical tank. You may be able to "tweak" the construction and decoration to fit the needs of your tank. These caves do not have to be made into towers. Also, as the fish mature, I can either use the towers in my other tanks or make new ones. Using a thin plastic sheet to make the floors and ceilings of the caves allows me the added function of cutting these sections out with a craft knife and making longer caves or tunnels if needed.

This project is rather simple but time consuming, so is the instructions. Please read this article in its entirety, including all the hints and tips along the way before you begin. You'll be glad you did.

Tools and Materials:

*Always wear SAFETY GEAR (safety glasses, facemasks and gloves) when using all tools. Especially POWER TOOLS. Please take note that if you use any tool in a way that deviates from its original designed use, it may result in damage to the tool or safety issues. If you are not familiar with the tools used in this construction method, you may want to ask for help from someone experienced in their use.



*™Sawzall with an 8 inch blade or a Hacksaw



Round File and/or Flat File or *Belt-sander (opt)

Measuring Tape


Sharpie Marker

Caulk Gun

Coarse Grit Sandpaper (3x8 inch sheet works well)

Box of Disposable Vinyl Gloves (This is absolutely necessary for this project.)

3-4 New or unused Paint Stir Sticks, cut in half ( Used to spread silicone.)

Long Nail (Used to close silicone tube so it does not dry out.)

1-2 Clean Buckets to rinse sand and gravel. (Old clean pillow case, to help rinse the sand.)

Utility Scissors

Hole Punch (The kind you use on notebook paper.)

Old Newspapers (The ink on older paper is less messy than newer paper.)

Freezer Paper (Get this at the grocery store.)

Small Soft Brush ( Throw away type. This is to gently brush away excess sand after drying and curing.)

Large Rectangle Container with a 3 inch depth to hold sand . (I used a ™Yaffa Store-Tote lid.)

Materials: (Try to decide the number of caves you will be making and the number of towers you plan to build.)

White PVC Pipe 4-inch diameter (See note under Marking and Cutting pipe sections.)

Approximately 10-15Lbs.(You may need more or less.) screened Play-sand or your choice of Aquarium Sand. (This sand should not be used in the tank when finished because it may have bits of silicone in it. Rinsing the sand will be discussed later.)

Approximately 5Lbs. of Aquarium Gravel (Same as in your tank.)

Aquarium Water Conditioner of your choice. (To treat the water you will be rinsing the gravel and sand in.)

Small mesh Plastic Canvas sheets (This is in the craft section of any department store. This is for the “roof” of each tower. I usually get about 3 circles per sheet.)

Stencil Making sheets. (This is in the craft section as well. Use clear or opaque sheets. If you cannot find this, try the office supply store for clear or opaque file folders. You will be cutting circles from these sheets to make “ceilings” for the caves. Each ceiling will be the next cave’s flooring. If you cannot find the plastic sheets. You can use the small mesh plastic canvas. There will be a note on how to do this. The number of sheets you need is determined by the number of caves you make. If a tower is to have four caves, you will need one plastic canvas ceiling circle and three plastic sheet circles, with the floor of the bottom cave being left open to the tank, thus four complete caves in your tower.) In caulk tube form. The amount varies for the amount of caves and runners you make. I used about 3½ tubes for 3 three towers and four runners. I have a total of 17 caves in my tank. It is important that you use safe products in your aquarium. After a great deal of research I went with the ™GE brand in the blue and silver tube (100% Clear silicone rubber for windows and doors.) I CANNOT GUARANTEE THE SAFETY OF THIS PRODUCT!! However, I can tell you how I decided on this brand. I researched several forums and websites that had several discussions about what brand is safe to use. I read several posts from people that had been using this product for years for building tanks. According to these people, at one time this product’s instructions stated that it was safe to use on aquariums. The statement was omitted after a number of lawsuits were placed by people that were using this brand to make two hundred gallon and above tanks. The tanks sprung leaks and the lawsuits went to court. Because of other info I have encountered, I suspect but have no proof, that GE probably makes some of the silicone we use from pet-store sources.

Aquarium Safe Silicone


Please read this:

So far I have not encountered any problems but this is the first time I have used this product. This, however, does not mean that it will be safe for use. If you use this product you do so at your Own Risk! Because this project relies heavily on silicone, you may want to price the product you plan to use. It is very important that you follow the drying and curing times that are provided by the manufacture and here within these instructions. Also make sure you work in a well ventilated area!


Cleaning and Rinsing the sand and gravel:

You may want to do this before you do any other part of this project so the sand and gravel will be dry. The sand can be slightly damp during application but not dripping wet.

Using your clean bucket(s), rinse your gravel well and spread it out in a single layer somewhere to dry. I would use a final rinse of treated water just to make sure there is no residue from chlorine and the like. You can also spread it out on some freezer paper, shiny side up to let it dry. I have heard about putting gravel in a low temp oven, but I have never done this. I really don’t see the need in this. The gravel does have to be completely dry to the touch.

Start with screened play-sand or the aquarium sand you prefer. Use treated water for the rinsing if you feel it is necessary. I used a clean, well rinsed, old pillowcase. You could go buy a cheap one and rinse it well in hot water to remove the sizing. (A product used in bed linens to keep it from shrinking too much.) The pillowcase goes into the bucket, then you add the sand into the pillow case. Rinse the sand in water and drain off. Do this several times. When the sand is clean pull the pillowcase out of the bucket with sand intact. Start twisting the pillowcase around. As it twists, the water will be pressed out. When you have a sufficient amount of the water out of the sand, dump the sand into the rectangle container. Smooth it out and let it dry.

Marking & Cutting the PVC Pipe Sections:

In my area you can only buy the PVC pipe in ten foot sections. I ended up using about seven feet. Also, I used the white PVC pipe because a plumber told me that the black pipe was not rated for drinking water in our area. I assumed that it might leach some chemicals into the water. Just to be safe you might want to check into this for your area. I choose the 4 inch pipe because it was easier to get the silicone and sand on the inside of the pipe sections.

*Always wear SAFETY GEAR when using all tools. Especially POWER TOOLS. Please take note that if you use any tool in a way that deviates from its original designed use, it may result in damage to the tool or safety issues. If you are not familiar with the tools used in this construction method, you may want to ask for help from someone experienced in their use.

With your pencil and measuring tape, mark off sections on the pipe. Choose sizes that fit with your fish. I made about six- three inch sections and about seven- four inch sections and two or three six inch sections. Cut sections with a *Sawzall tool with an eight inch blade or use a hacksaw. Cut sections as evenly as possible. Once the sections are cut, stack the sections on top of each other to see if each section is level. If not, use a *Belt sander or a file to smooth off the edges to make sections set level when stacked.

Cutting the six-inch runner caves:

You will need to make a paper pattern. Set the end of a pipe section on the paper and trace around the pipe. Cut out the circle pattern and check to see if it fits the same size of the pipe. Adjust the pattern if needed. Fold the pattern in half. Make sure the edges meet and the fold is even. Unfold the pattern and place on one end of the pipe section. Mark the fold line onto the pipe section on both sides of the crease. with a pencil and straight edge of the measuring tape mark lines down the both sides of the pipe section. check the other end of the pipe section and adjust your lines if needed. Cut the pipe sections on these lines with a *Sawzall with an eight inch blade or with a hacksaw. Make cuts as straight as possible. Clean and level the cut edges with a *Belt sander or file. Check to see if the runner caves will set level and adjust as needed. You can also make these sections bigger (to adjust paper pattern, mark off 1 inch from the edge and fold). Instead of a 2x6 inch runner cave, you can cut off a one inch section and the runner could be a 3x6 inch cave, or whatever size you need. After the sand applications these can be stacked and silicone together to make a solid runner cave piece (stacked in pyramid fashion) in the tank.

Cutting the entrance holes for the caves:

With a Sharpie marker draw an irregular circle in middle of cave section. Draw it slightly off to one side or the other. I alternated the sides. One opening to the left and the next cave’s opening to the right side so the fish will not be right on top of each other when entering the caves. Make the cave openings large enough to fit the size of your fish. Don’t forget to allow for the fish’s growth. *Drill a hole near the marked line big enough for the *Jigsaw blade. Use a Jigsaw to cut the opening following the outline, taking off the marked outline. Use a round file to smooth out the edges or to open up the entrance a little more if needed. The irregular shape looks more natural than just a round opening.

Rinse and dry the cave sections. Take coarse sandpaper and run it over the inside and outside of the sections. You just want to break up the slick surface of the pipe. Once again, rinse and dry the cave sections. Now is the time to double check your cuts and adjust them.

Setting up your work area:

While this project is rather simple it is time consuming because of the drying and curing times. You will want to set up your area somewhere where you can allow the cave sections to sit and dry between applications and to cure when completed. Make sure the area is protected from bad weather and is well ventilated, (silicone stinks!) You may want to use the disposable face masks. This work area is where you will be applying your silicone and sand layers and building the cave towers.

You will want to spread a few layers of old newspapers over your work surface. Next cover the newspaper layer with an overlapping layer of freezer paper, shiny side up. The silicone, when dry does not stick to the thin plastic coating of the freezer paper. You will want to keep your sand container to one side. Pick out one section to use as a palate for the silicone. I found it easier to squeeze out a 3-inch wide section of silicone onto the freezer paper and then, using a paint stir stick as a spatula, spread an even layer on the sections. Keep your silicone palate free of debris.

A note about drying and curing times:

Before we begin applying layers of silicone and sand, I want to point out how important drying and curing is to this project. Silicone tends to shrink some as it is drying. It is very important that each application of silicone-sand layer be allowed to dry for at least 24 hours. If any shrinkage occurs you can add a little more silicone to the exposed area and some more sand. Unless there are large areas of shrinkage, which need to be retouched before proceeding, you can wait until the decorating phase of the construction to add more sand and some rocks to exposed areas. It is important that there is complete coverage of all areas of the cave section.

The recommended time frame for curing with the brand of silicone I used is 72 hours dry and 24 hours soaking in treated (use your water conditioner for your aquarium) water with some water changes. This not only allows the silicone to dry and cure, but for the smell to dissipate and any chemical residue to be removed before it is put in the tank.

Applying silicone and sand:

Put on a pair of disposable vinyl gloves, (change often).

Follow the instructions on the silicone tube for using the caulk gun. Squeeze out about a three-inch section of silicone on your palate (repeat as necessary). Using your paint stick as a spatula spread about a 1/8th to 1/4th inch layer of silicone onto the inside of the pipe section. The layer needs to be thick enough to support a good layer of sand without being bulky. Spread the silicone over the entire inside section before adding sand. Make sure to get the silicone right up to the edges both top and bottom. Hold the pipe section up in the light so you can check for spots that are not covered with silicone. Also, add silicone around the inside and outside edges of the entrance opening.

Once you have a complete layer of silicone on the inside of the pipe section sit it (wall side down) in the sand container. Start packing sand on top of silicone, gently but firmly. Turn the pipe section a little and pack more sand on section. Continue this process until the whole inside of section is covered in sand. Gently tap the cave section to remove some excess sand. Holding the pipe section by the edges, repeat the process on the outside area of the section. Place the section somewhere to dry for 24 hours. Repeat the process until you have all the sections ready with the sand layers.

For the runner caves it is just a matter of spreading the silicone on both sides and covering the layer with sand. Sit the runners to the side somewhere to dry for 24 hours. After the cave sections have dried for 24 hours, check for large exposed areas, and touch up. Dry 24 hours for all touch ups. When sand layers are complete gently brush off extra sand. Do not be alarmed at the amount of sand that comes off the cave sections.

Sand layers completed.


Runner caves, see how these could be stacked?


Attaching the ceilings to the cave sections:

The towers consist of a plastic mesh canvas ceiling on the top cave so some type of plant like Java Moss can be tied to it with fishing line. This would give the towers a Spanish moss affect as the moss grows. You could also silicone sand or rocks to the ceiling if you prefer. The bottom side of the bottom cave is left open so it can be surrounded by the substrate making it more secure. The gravel will be the floor of this cave. The ceiling of the middle caves will be the floor to the cave above it. The bottom cave receives a ceiling as well.

First stack your cave sections in towers to see how many ceiling sections you will need to cut from the mesh plastic canvas and solid plastic sheets. Take a cave section and sit it on the plastic sheet. Trace an outline around the cave on the sheet. Be careful not to mark on the cave section. Cut out the circle and use as a pattern or just use the cave section to trace the other plastic sections. Once you have the ceiling sections cut you are ready to fit them to the individual caves and glue it down with the silicone.

Plastic mesh canvas

Following the diagram below, trim the plastic ceiling sections to fit midway inside the rim.

Once the ceiling sections have been trimmed, take the sand paper and sand both sides of the solid plastic sections and wipe off residue. This helps with the adhesion of the silicone and blocks the view of the fish in the caves below or above. Using the hole punch, punch a hole in each solid ceiling section. Place the hole about ¼-½inch past where the inside edge of pipe section will meet the plastic sheet. This hole is to help the water flow through the caves. If you are using the mesh plastic canvas, you will need to build a layer of silicone and sand on the top part of the sheet. Sit trimmed piece on freezer paper. Spread an even layer of silicone over the mesh. Sprinkle sand over the silicone pat down gently. Let this layer dry completely then gently peel the whole ceiling section off the paper. Use the nail to poke a few holes in the ceiling.

(TIP: Always make sure to touch the tip of the tube nozzle to the object receiving the silicone to get good contact between the object and the bead of silicone.)


Run a medium size bead of silicone around the rim of the pipe(cave) section

approximately where the plastic sheet will meet the rim. This way silicone will be on the inside and outside edge of the plastic sheet. Line up the plastic ceiling section, with the punched hole on the opposite side of the cave entrance. Then gently place ceiling section in place and tap gently all around the section to get good contact. Smooth out the extra silicone that is on the outside by spreading it evenly over the plastic ceiling section and the rim of the pipe section. This way there is no lumps of silicone that can make the caves fit unevenly when building the towers. The middle cave ceilings are done.

For the top cave of the tower that is receiving the plastic mesh ceiling sections, do the same as above, except do not add the silicone and sand layer to make a solid section, this is for middle caves only. When you are tapping the ceiling section down, make sure the silicone seeps through the holes of the mesh plastic so good contact is made. Then very gently spread out the silicone, just to smooth it out. Take a small amount of sand and gently pour it over the silicone and just gently pat it down. Do this for the ceiling cave of the towers only. If you plan to do sand and rocks on top instead of the moss, skip this step.

Now the caves are ready to sit and dry for at least 24 hours. Longer depending on the humidity in the air.

Individual caves

As you can see in the picture above, I did not worry to much about the extra sand layer that ended up on the edges. Make sure you get a good size bead of silicone around the rim and there is good contact or this will become a problem.

Building the towers:

After the ceilings are completely dry it is time to build the towers. You’ll have to choose the number of caves to use for each tower. You can build the tower as tall as your water level in the tank or use the caves as single floor caves. Tall towers may need to be anchored with counter weights depending on how stable they are. I would not go over 18-inches just to be sure. Make sure you end up with the cave with the mesh plastic ceiling on top of the tower.

Select the bottom cave. Run a ½ inch thick bead of silicone around the rim of the cave section covering to the outside edge of the rim as well as some of the ceiling’s edge, take care around the punched hole. Line up the bottom (open end) of the next cave over the bead of silicone adjusting the entrance opening to be offset from the bottom caves entrance. Evenly sit the cave down on the bottom cave. The silicone will ooze to the outside edge and the inside edge as you gently but firmly press down. Just gently spread the outside silicone across the seam, with a paint stick to smooth it out. leave the inside seam alone. Repeat this process for each additional cave until the tower is complete, with the top cave having the mesh ceiling. Gently slide the tower over to one side of your work area and leave it to dry for at least 24 hours, 48 hours would be better if you can wait that long. Now that the towers and runners are done you can decorate them. First you will cover the seams where the caves were joined. Simply spread just enough silicone over the seam to hold sand. Sprinkle sand over the silicone and pat down gently for good contact. Do each complete seam on the tower and let dry for about two hours or to the touch. Very gently brush off some excess sand. Once the seams are covered on the towers you are ready for the decorative rocks.

Decorating the cave towers and runners:


First check areas for shrinkage. These areas will help determine where to add the rocks. Lay the tower down on its side and prop it up next to some crumple newspapers or aluminum foil. You will need to apply a really thick bead of silicone to the tower covering the shrinkage area. Apply the rocks, making sure to make good contact with the silicone by packing them down into the silicone. Some rocks may fall off. After you have applied the rocks, sprinkle sand over the silicone and rocks and with a patting motion embed the sand into the silicone. You may need to stand the tower up and hold it by the top and tilt it so you can apply more rocks and sand in different areas on the tower. You can come back about 15-30 minutes later and gently brush off some excess sand off the rocks. The rocks will look like they are encrusted and some of the silicone will be camouflaged. If you are not sure where to place the rocks, just imagine the tower being under water and all but a few layers of rocks have been washed off over time. Make sure to balance out the rock layers, so that one side will not be heavier than the other, it might tilt over to one side in the water if one side is heavier.

If you are not going with the moss look on the top of the tower and have decided to go with sand and rocks, just spread some silicone over the ceiling and add some rocks and sand. Have the rocks tumbling down over one side. Make sure to leave some of the mesh open for water flow, or if you used a solid ceiling section, do not cover the punched hole. To decorate the runner caves, just follow the same procedure making sure to leave an area on the top so it can be stacked if you decide to do so.

Completed runner caves

When all the decoration is complete, sit the towers and runners off to one side of your work area to dry and cure. Please follow the recommended times and procedures discussed earlier. Before soaking in the water treatment, gently brush off any excess sand. Although there is sand embedded into the silicone, you will always get a small amount of sand coming off when you brush it. Don’t be alarmed by it. You just want to get rid of any real excess amounts so your water will not become cloudy. Next soak the tower and runners following the earlier recommendations. They are now ready for the tank. I ended up not putting the towers in front of the intake tubes because the gravel in my tank was rather large and it just did not feel secure enough to hold them in front of the down flow of the power filters.


Home Sweet Home


All images and text on this page are © Tam-Tam.

Articles Index / Do It Yourself Index
This article has been viewed 30247 times

Site Index / Articles Index / Product Reviews



Cash Us On:

FacebookVisit PetFish.Net On Facebook YouTubePetFish.Net Videos On YouTube TwitterVisit PetFish.Net On Twitter Google PlusVisit PetFish.Net On Google+ RedditVisit PetFish.Net On Reddit PinterestVisit PetFish.Net On Pinterest

How Bou Dah?


PetFish Index
About Us
Contact Us

All Articles Index

The Fish
Barbs, Tetras And Minnows
Catfish and Loaches
Freshwater Sharks
Goldfish, Ponds And
Coldwater Fish

Killifish Care
Killifish Species Profiles
Miscellaneous Fish
Native USA Fish
Saltwater And Marine

Other Fauna

Aquatic Plants

Aquarium Basics
Foods And Feeding
Live Foods
Diseases And Fish Health
Spawning And Fry Care
Fishy Fun Stuff

Do It Yourself
How To Guides

Products And Services Reviews

PetFish Video

Our Free Ebooks

Conversions Volume Calculator

Aquarium Measurements And pH Scales

The Ultimate Aquarium Calculator

Made with Aquarium Designer
Design Your Aquarium

Link to

Translate To

© Since 1996, PetFish.Net All Rights Reserved
All content is copyright by and/or the named author and may not be used without written permission.
Privacy Statement - Contact Us - About US - Links - Site Map

Sponsored In Part By