In many years of SCUBA diving on tropical reefs and in my local New York water I noticed there is something glaringly absent from most of our reef tanks. We tend to use smaller roundish pieces of coral rock because that is what is generally available for sale. In a natural reef, however, especially near shallow water or close by to a shipwreck, you will notice thin calcium encrusted formations that may have been rigging on a ship or construction debris. These items in tropical seas eventually become encased in calcium- along with life forms associated with such structures. Although interesting, these fragile items do not ship well and are not collected or sold. Fortunately, they are easy to build and the natural items can remain in the sea to provide hiding places for fish and to provide an even more varied panorama for the occasional SCUBA diver.

The materials are very inexpensive and can be obtained at most hardware stores or home centers such as Home Depot. For a rock about one inch thick and four feet long you will need a ten foot piece of PVC pipe, a couple of square feet of plastic window screen and the smallest bag of “sackrete mortar mix” you can find. You will also need a glue gun and a small propane torch.

First cut the PVC pipe about 12” longer than the rock you plan to build. Drill ¼” holes all over it about an inch apart. (You do not have to use a ruler on any of this just, estimate.) Then go outside, where there is a water hose nearby. Wearing gloves, heat the pipe gently in sections with the torch until it bends. If it starts to burn, spray the hose at it and go slower, you don’t want to inhale burning PVC fumes so try not to heat it so much that it catches fire. Gradually keep heating and bending the entire pipe until you have a very crooked looking, uneven item that does not look like it was made on purpose. You can even bend it around on itself but whatever you do remember that straight lines do not occur in nature. Neatness does not count, the opposite is true. When you think it is bent enough, bend it some more. After each bend, you can put it in cold water or shoot a hose at it so it keeps it’s shape. Now make another shorter piece the same way and using the torch heat one end and flatten it. This shorter “branch” can then be tied to the first piece with fishing line or plastic tie wraps. I like to use plastic screws and nuts. Any number of pieces can be connected to the main piece to achieve the finished product that will fit in your tank. Next cut the plastic screen into strips about one inch wide. Wrap the strips around the bent pipe holding it in place with hot melt glue. The screen is there to help the mortar stick to the PVC. It is best to wear disposable plastic gloves for this next step because the mortar will really dry out your hands. Mix the mortar to the consistency of thin toothpaste and place it on the wrapped pipe. Most of it will fall off but that is fine. You just want to get a thin layer of mortar to stick. When the entire piece is coated, wash up and go look at your fish tank for a day or two while this cures. Every two days or longer put another layer of mortar on the structure until you have built it up to about an inch. Keep it damp between curings or the mortar will be very weak. Now comes the creative part. For the final layer mix the mortar a little stiffer and blob it on in ways so that it sticks out and looks unnatural. Stick holes in it with a pencil or toothpick. When you feel an urge to smooth it out because it seems as though a piece will fall off you’re finished.

After two days place it in fresh water to cure. It will have to cure for a few weeks before you can put it in your tank, not because the mortar will crumble, but because the cement in mortar contains lime and it will affect the pH of your water. After a few weeks put the piece in new fresh water and check the pH. In a couple of days check the pH again. If it has not changed it is safe to put the piece in your tank. Coraline algae will grow on this home made rock much faster than on real rock and in a month or so you will not be able to tell the difference in the rocks you built and the ones you bought, except for the fact that the ones you made are much better looking.

A homemade, hollow 3' long PVC/cement rock completed over can be seen to the right of moorish Idol.



Homemade, hollow PVC/cement rock, during construction


Finished PVC rock.


Acrlyic skeleton used for smaller thinner rock instead of PVC.