Everything You Need To Know About Live Rock

Every reef is built upon solid rock. It’s not quite the same as the rock you might find in your backyard, however. Instead, it’s rock that has literally grown in place as corals have lived and died. Over countless seasons the skeletons these corals leave behind accumulate and eventually fuse to become solid rock. But, solid as it may be, this rock is still fairly soft and so, quite commonly, pieces of it break free from the reef- most often during heavy storms. These broken bits of rock are what is collected and sold as live rock. The rock itself is no longer alive. However, it is teeming with life. This life offers all sorts of benefits to the aquarists from improving water quality to providing your fish and corals with a home away from home to being just plain gorgeous.


Live rock is home to all sorts of wonderful and beneficial lifeforms. Probably the most obvious is coralline algae. Good quality live rock will be covered in the stuff giving it a pink to purple coloration. Unlike most algae this is one you actually want in your tank. It’s an encrusting type of algae that leaves behind a calcareous skeleton much like coral- hence the name. In fact this algae contributes a fair amount to building the reef rock itself and can actually fuse rocks together over a long enough time in your tank. So why would you want this algae? For one, it’s beautiful. Purple is the most common color followed by pink.

However, it also comes in lots of other colors including red, green, blue, and yellow. Besides the looks the other benefit is that it can out compete the less than desirable algae. Coralline algae will encrust over the bare rock leaving nuisance algae nowhere to grab hold.

There’s a lot more than just coralline algae living on, and in, live rock, though. It abounds with all sorts of tiny shrimps, crabs, worms, sponges, snails, and other interesting sea creatures. All together the wide variety of critters found on and in live rock can begin to build an actual food chain within your tank- ending with your fish and corals getting a healthy source of live food.


Beyond the looks and the free meals live rock actually also serves a very important role in filtration. As it is incredibly porous it provides loads and loads of surface area to grow beneficial bacteria. A healthy and strong biological filter is extremely important in marine aquarium setups and live rock offers the perfect solution. Indeed in a marine tank the bulk of the biological filtration can actually be handled by a sufficient amount of live rock. Of course supplementing it with other sources doesn’t hurt either.

Natural Beauty

The last important reason to use live rock is purely for aesthetics, both for you and for your fish. When keeping fish in captivity one of the goals should be to provide them with an environment that feels like home. There’s no better way to accomplish that than to provide them with what is essentially a literal chunk of their natural habitat. Reef fish spend their entire lives in close proximity to the rock that forms the reef’s foundation and rely heavily on it for food and shelter. It’s an integral part of their lives. When keeping a marine tank the goal of most aquarists is to achieve something resembling nature and live rock fits the bill quite nicely.

So, when you go shopping for live rock for the first time you may be a bit lost on what you should get. Even with something as simple sounding as rock there are quite a few options. The options relate mostly to where the rock originates from as well as how much work has been put into getting it ready for your tank prior to your purchase.

Cured Or Uncured

When live rock is collected and shipped it is typically packed in bags with a minimal amount of water- really only enough to keep the rock moist. As a result when it arrives at its destination a large percentage of what was alive when it was collected has died. As you can imagine this makes it less than suitable for placement into your tank. The process of cleaning the rock up and getting it ready for entry into your tank is known as curing. The basic idea is to place the rock into a bare bones setup and let the die-off happen. The rock is regularly cleaned and eventually stabilizes and the life begins to regrow at which point it’s ready for the main display.

So when you shop for live rock you are likely to see both cured and uncured rock for sale. Knowing what curing is, these names are pretty straightforward. Do note that cured rock can only be placed straight into an established tank if it is purchased locally, though. Any shipped rock, cured or otherwise, will experience die-off and so will need to be recured. The process will be much quicker with rock that was cured before shipping, however, and if you can get cured rock from a local store it can go straight into your tank.

So, why would you want to buy uncured rock? Cost. Uncured rock is much cheaper. The downside is of course that you need to do the curing yourself. It’s not a difficult process, although it does take a few weeks and can be a bit messy. As a side note uncured rock can also be quite interesting. You truly never know what will emerge from the rock as the process proceeds.

Types Of Live Rock

There are a few types of rock as well that you are likely to encounter when you begin shopping. For the most part the difference between the types refers to the location from which they were collected but there are a few other categories to look out for.

Base Rock

When live rock starts to accumulate in the sand surrounding the reef some of it naturally ends up on the bottom of the pile. This rock has essentially the same structure as normal live rock and is loaded with beneficial bacteria just the same, but is more or less bare on the surface. This of course makes it rather bland to look at, but on the plus side it is cheap. So why would you want it? Well, when you start piling up the live rock in your tank you’re likely to need some pieces to form the foundation. Using base rock for this means less of your beautiful top quality rock has to get buried.

Pacific Live Rock

Typically you will see Pacific rock sold under the name of the island it hails from- most commonly Fiji live rock. You may also occasionally see rock from Tonga, the Marshall Islands, or Indonesia. The rocks from different locations can have different appearances that can be great for achieving just the right look in your tank. Tonga live rock, for example, is often very branch-like. Pacific rock is generally the best quality as it is very porous and often loaded with all sorts of interesting creatures and heavily encrusted with coralline algae. When shopping for live rock this is most commonly what you will see.

Caribbean Live Rock

Also sometimes labeled as Atlantic or Gulf rock, or after one of the various islands in the region, Caribbean live rock comes from, well, the Caribbean. Quality can vary quite a bit from the different locations, but in general Caribbean live rock is more lackluster in appearance and often a bit on the heavy side. The price usually reflects this, although it’s not actually that common to even see it for sale anymore.

Aqua Cultured Live Rock

The aqua culturing process for live rock works a little different than it does for fish or corals, which is done fully in captivity. The process for live rock actually takes place in the sea. Terrestrially mined rock, usually limestone or something similar, is deposited on the sea floor and left to be colonized for a year or more. This is a more eco-friendly option compared to harvested natural rock but the drawback is the quality. The majority of aqua cultured rock comes from the Caribbean so much like natural Caribbean rock it lacks the diversity you see in Pacific rock. Furthermore, it lacks much of the complex shapes you see in natural rock. Finally, depending on the type rock that was used it may be very heavy and rather non-porous.

So, how much rock do you need? Around 1 to 2 pounds per gallon usually does the trick. However, as a natural product, the density can vary quite a bit and so it may take more or less to achieve the desired look you’re going for. The shape of your aquarium may affect how much rock you need as well.

The creatures of the reef are tightly woven community- reliant on one another for their very survival. And while recreating the diversity and bounty of the ocean within the confines of a small glass box situated in your living room is nigh impossible, it is always the goal. Live rock delivers an entire community of mircoorganisms to your aquarium and brings it closer to being a true ecosystem than any other method. Likewise, there’s no better way to recreate the visual aesthetics of the reef than to use what is essentially actual pieces of reef. It’s like having your own little spice of the ocean to admire.

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