Live and non-Live Rock – Natural and Artificial

by Albert J. Thiel


Cycling one’s tank is probably the most important matter that a hobbyist needs to take care of and for the most part this is now done by initiating the Nitrogen cycle using so  called live rock or other types of rock that are currently available in the Hobby.

Most Hobbyist are aware of what needs to be done to make the process start, and in most cases will use so-called “live rock” to do so, basically reef rock on which there still is a lot of live growth of various kinds, often a number of sponges, small polyps, and the like. Note that live rock is also a major cause for the so-called hitchhikers to enter your aquarium. These can include polychaete worms, flatworms, small sea stars (Asterina sp.) and a number of other HH’s (Hitchhikers) as they are referred to.

There are many kinds of live rock available in the trade, and which one to use is really a matter of personal choice and of availability in the area where the Hobbyist is located, unless they order it from one of the online sellers. Ordering online is definitely an option, but since live rock is not inexpensive to begin with, and since most types are heavy, ordering online can set you back quite a few dollars especially if your reef tank is fairly large. It is therefore better I believe to find a store that is local to you or not too distant from where you live that carries live rock and purchase it there.


Live rock after it has cycled. Photo credit: Sam Parker 

In addition to live rock Hobbyists also add so called live sand to their Aquariums, sand that already contains a number of bacteria that can process the organic material that is present in the tank, or added to it, and get the cycle to start running its course. Often live rock and live sand are added to the tank at just about the same time, and since live rock has growths on them that will die off and start the cycle, and since live sand has both organisms in it that will die and decompose, but also has beneficial bacteria already that will help the cycle progress, adding both at the same time is definitely a choice that many go with.

Even though a lot of the growths on the live rock and in the sand will die off during the cycle, there are quite a few organisms that will not and that will show up one day in your tank, and you will wonder where they came from. Well they came in on the rock and in the sand and made it through the cycle, and are the hitchhikers I referred to earlier.

It should be noted though that a recent trend that has emerged is running tanks with bare bottoms (nothing on the bottom of the tank), meaning no substrate at all. Often in those cases (BB’s or Bare Bottom Tanks) Hobbyists will populate the bottom of their Nano-Reefs with a number of life forms, in many cases Zoanthids (Zoas) and Palythoas (Palys) and the like. As they spread and multiply, they end up covering the entire bottom of the tank or most of it. 


So what types of live rock is available to Hobbyists?

Below are just a few of the many types that can be purchased from local pet stores, usually referred to as local fish stores (LFS) or from online resellers:

  • Fiji live rock

  • Totoka live rock

  • Florida rock

  • Caribbean rock

  • Vanuatu rock

  • Tonga rock

  • Base rock

  • Pacific rock

  • Atlantic rock

  • Reef rock

  • Cultured rock

  • Base rock

  • Artificial rock

  • Cured rock

  • Uncured rock

  • Eco-rock™

  • Tonga rock

  • Aqua-Cultured Rock

And even more, as you would find out if you did searches on the internet for live rock.

Cured and uncured rock 

There is another very important factor to consider however, and that is whether the rock you are going to use has been “cured” or “not cured”, as noted in the list above. There even is a category referred to as “pre-cured”. It is also important to know what the seller of the rock you are buying actually means by the terminology he or she is using. You would imagine that everyone means the same thing when using a particular name for a piece of rock. Indeed that is what would make the most sense but unfortunately that is not how it works. Different vendors mean different things with the same terminology so an educated Hobbyist will do well to ask the question and know exactly what he or she is getting, so they know what may still need to be done to be the rock usable and safe for immediate use. Often none of the rock sold and bought is in my opinion ready for immediate use. It is therefore best to place it in the Nano-Reef and test for a day or two, or maybe even a few more to make sure that no ammonia and nitrite appears when testing is done.

What is uncured rock, and how do you cure it?

Cured rock is live rock, the variety that has life forms on it, that has been kept in a container of some sort, and kept in kept there for a few weeks till all the growths on it died and decomposed, and while that process is going on beneficial bacteria grew on it that eliminated any ammonia and nitrite that came about from all the die-off. This is basically the process part of  the Nitrogen Cycle that as you know explains how that process starts, and how it evolves towards completion.
Whatever is still alive on and in the rock dies off as the rock is placed in saltwater in a container of some sorts, and just left sitting there till all the life forms die and decompose, while beneficial bacteria grow on it and populate the rock.
Once that has happened the rock is ready to be placed in the tank, as it should no longer produce a cycle, and if it does it will be a minimal one that all the bacteria that are now on and in that rock can easily deal with, and convert ammonia to nitrite and then to nitrate.

Curing live rock

If you plan to “cure” your live rock yourself, here is what you need to do:

  • Purchase the needed quantity based on the size of your Aquarium (the general recommendation is from ¾ pound per gallon to 1.5 pound per gallon – I tend to prefer the lower end of that recommendation). Place all the rock in a container with saltwater and put an air stone in it, and gently bubble some air from the bottom to the top.


  • Close the container by placing a lid on it or something that will keep the rock in the dark. Let stand for about 3 weeks or so and then test for ammonia and nitrite. If any is present the rock has not fully cured yet. Leave everything at it is for another few days and test again. Once ammonia and nitrite test at 0.00-ppm your rock is cured and is ready to be used.


  • Rinse the rock real well in clean saltwater and remove (brush off) any material that is still attached to it, but do so gently, no need to use a stiff bristle brush. All you want to do is remove any visible dead life forms that may still be attachedto the rock. Do clean it very well though and rinse it a few times in saltwater that you have in another container to make sure that anything that needs to be removed is removed.

Your rock is now cured and ready to be placed in your Aquarium, and is now populated with millions of bacteria that will perform as intended and as explained in the Nitrogen Cycle section discussed earlier, meaning they will convert ammonia to nitrite and other bacteria will nitrite to nitrate. Now does that mean that when you put it in the tank that you will not get a spike of ammonia at all? You should not, but it depends on how clean the rock is when you put it in the tank, and whether there is anything left on it that can break down and decompose. More than likely you may see a small amount of ammonia, but with all the bacteria on the live rock, it should not be a severe one and should be converted further by the bacteria and end up as nitrate in a very short period of time. You should be able to put life forms in the tank soon after you add the rock, but I suggest you go slowly about it, and not put too many in at the same time, just to be on the safe side. Patience is always needed in this hobby and something we need to develop if we don’t have it and if we want to rush into doing things. Going too fast can lead to problems and loss of life forms, even when you have a tank that is fully cycled and has aged for a while. In my experience, the slower you go in adding corals and fish, the better off you will be. Many hobbyists want to get their tanks filled with all sorts of life forms and that is understandable, but going to fast is not a good idea at all, in fact it is a very bad idea

So what is Cured Rock?

Cured rock is rock that has gone through this process before you purchase it, and that is ready to be placed in your tank when you receive it from where ever you buy it from, whether a local LFS or from an online source. In essence someone else has done the curing of the rock for you and you no longer need to worry about curing it yourself, or so it should be, because there is a caveat.
Note that the some degree of caution applies: the same as the one I mentioned above: do not add too many life forms at once as you may get a mini spike of ammonia, as even the cured rock you buy may still have some dead material on it that will decompose and cause that spike. Why would that be so? Well depending on who cured your rock it may not have been left in the curing vessel for long enough, or more than likely it may not have been rinsed and cleaned well enough once the cycling was completed. Since you do not know how well both of these processes were taken care of, it pays be careful and not take any risks.

If there is an ammonia and/or nitrite spike, and if during that spike you have sensitive life forms in the Nano-Reef you may end up with problems that result from the presence of ammonia and nitrite in the tank’s water. Going slow in adding life forms, therefore, tends to be a lot safer as the risk of those organisms adding even more ammonia to the tank is basically minimal, or minimized, and should allow the existing bacteria to deal with it and convert it to nitrite, while other bacteria turn it into nitrate.
Hopefully the live rocks will have enough bacteria on them so no mini-cycle occurs when you place that rock in your tank. And if it does, with all the bacterial growth that already exists on and in the live rock, the small cycle that may occur (ammonia appearing and maybe some nitrite) should be neutralized fairly rapidly, very often in 48 hours or even less than that. All you need to do to make sure it does not, is to run an ammonia and nitrite test 48 hours or so after you first place the rock in the tank. If you get a 0.00-ppm result you know that the tank is ready for your first fish or coral. Below are some pictures of uncured live rock looks like, and then below that rock that has been placed in an Aquarium for some time and on which a good deal of coralline algae has started to grow.

Lots of Hobbyists wait and wait for coralline algae to appear, and sometimes they do and sometimes they do not appear, even after weeks and weeks. The main reason for this is that coralline algae starts to grow when you have some pieces of rock in your tank that have some coralline algae on it already, or when you “seed” the Aquarium with a small piece of rock that has coralline algae on it.Once you do so, and if your calcium levels are in the right range (e.g. 420-450ppm), coralline will take off and grow in more and more places. Note that coralline algae come in more than just the purple color.. They can be red, yellowish, blue, pink, gray-green and more Purple Plate Coralline Algae on Live Rock

Using Non-Live Artificial Rock

Some Hobbyists use rock that is actually not live rock, but that is artificial, or is totally dead aragonite based rock that may come from a reef but that, obviously,does not have any life forms on it that will die and decompose.Some actually use a mixture of live rock and non-live rock. Let’s deal however with the use of non-live rock (dead rock or artificial rock).

When you start your reef or Nano-Reef with such rock, since nothing will break down and start the Nitrogen Cycle, you will need to add some organic material to the tank so the cycle “can” start. You can use anything that is organic, e.g. fish food you have, a piece of shrimp that was for human consumption, flake food, or anything else that will decompose once it is in the water.How much you add really depends on how large your tank is. In a Nano-Reef, which is the real topic of this book, my suggestion is that you add about three quarters of a teaspoon of whatever it is that you are going to use., as that should be plenty to start the Nitrogen Cycle. That should be enough to get things going and get the let’s call it “dead rock” seeded with the bacteria, bacteria that will develop as a result of the ammonia and multiply quickly, followed by the ones that convert the ammonia to nitrite and then eventually more of them that take the process yet one step further and bring about the nitrates. Once that happens the Nitrogen Cycle has started, and you are on your way to have a tank that will be ready for life forms about three to four weeks later (more likely four than three in my experience). So what does the so-called dead rock look like? Depending on whom you buy it from and depending on whether it is actual reef rock that was bleached “to death” until it has nothing left on it and is totally white or just about, it will take on different shapes and looks.

Mixing Live Rock and Dead Rock

When live and dead rock are mixed there is no need to add any organic material to the Aquarium, as whatever is still present on the live rock that dies off will start the cycle, and both the live rock and the dead rock will slowly be seeded with bacteria, as explained under the Nitrogen Cycle section and under the Liver Rock section above. How fast the seeding with bacteria takes place is hard to tell as too many factors are involved that determine how fast it will actually happen. What can often be done when more rock is needed in a tank, or when upgrading to a larger system, is to add dead rock rather than live rock to make certain that no secondary cycle suddenly starts, as the dead rock does not have anything on it that can die off and produce decomposing by-products.

Should you have any  questions feel free to let me know via
Happy Reef keeping !
Albert J. Thiel


About the author 

Albert J. Thiel is the founder of legendary Thiel AquaTech (Active during the 90's) and a pioneer of many of the current reef keeping methods widely used today. Albert has been invited as a guest speaker to may international aquarium conferences and In 1989 he published possibly the first book on what we now call ‘nano reefing’ entitled, Small Reef Aquarium Basics – for smaller tanks and for beginner hobbyists. Other notable works include  The Marine Fish and Invert Reef AquariumAdvanced Reefkeeping IAdvanced Reefkeeping IIThe New Marine Fish and Invert Reef Aquarium.