Live rock is a very important aspect of a saltwater aquarium. It is a vital part of a natural aquarium. It alone can be all the filtration needed in well balanced saltwater aquariums (although I don’t recommend this). I consider live rock to be 80% of the filtration in a saltwater tank, the rest coming from the protein skimmer and refugium.
What is it?
Live rock is calcium based rock (coral rock) that was in the ocean and found around and among a reef. It usually won’t have actual corals on it, but it will have nitrifying and denitrifying bacteria and all sorts of other beneficial organisms such as small invertebrates and filter feeders (sponges, tube worms, etc.), good worms, pods (copepods, amphipods, etc.), and much more.
What’s so Good About it?
Live rock is so important because it is the base of the whole system. It houses bacteria, provides a base for corals, and shelter for fish. It is the entire structure of a reef.
Although it is possible to run a saltwater tank with nothing more than live rock, powerheads, and water changes, I don’t like to push the limits. This is just inviting disaster. I put too much effort and money in to a tank to risk losing it all by trying to prove the simplest method possible is actually possible. In my experience tanks with a protein skimmer tend to be more stable, more resilient, more forgiving, and less susceptible to crashing and other similar disasters.
It is possible to get pests from live rock, but this is surprisingly rare. Possible pests are undesirable crabs, fire worms, aiptasia, etc. In most cases it isn’t an issue, but if you have any pests you want to get rid of them as quickly as possible. Aiptasia can be killed with Red Sea’s Aiptasia-X, or injection of things like kalk solution. Worms can be removed manually with hemostats (DO NOT TOUCH them with your bare hands) or you can use a worm trap. Crabs can be more of a challenge. You can remove the rock they are hiding in and get them out with hemostats, or use a DIY trap using a 2 or 3 liter soda bottle.
How Much?
The usual recommendations for live rock are 1-1.5 pounds per gallon. I recommend aiming for 2-3 pounds per gallon. I like to have a lot of it, it is just that much more filtration and shelter for fish. If fish feel they are always within an easy shot of a place to hide they are actually more comfortable coming out and exploring the tank. And since the live rock is 80% of your filtration, it is good to have more.
Not all of your live rock has to start out live. You can easily have as much as 75% start as dry, dead rock. As long as the rest is good live rock it will spread and it will all be live in time. It usually takes about six months or so to not easily tell what started out dry. It will even seed your sand bed. You can buy dry base rock by the case for $2-3 per pound, and even make your own. Making your own rock is a fun project that will allow you to make rocks of the exact size and shape you want. Recipes can be found online (usually a mix of cement and crushed coral/aragonite).
What Kind?
Not all live rock is equal. There is base rock, low quality rock, high quality rock, aquacultured rock, and an endless supply of rock from specific areas around the world. I don’t get caught up about the exact collection location, I go by how it looks and how porous it is.
There are two main factors you want to look for when judging how good live rock is, porosity and life. Very porous live rock means there is more space for bacteria to colonize, as well as all the good stuff that grows in and on the rock (sponges, bivalves, good worms, etc.). It even gives more places for the inhabitants you add to hide (small fish, shrimp, small crabs, etc.). It can be porous with lots of big nooks, crannies, and tunnels, or it can have lots of small holes and tunnels (fish and crabs may not be able to get in, but water can run through the rock and it can house bacteria). In addition, not only is the porous rock better, but it is cheaper too since the same size rock that is less porous will weigh and cost more than the same size rock that is very porous.
As far as life goes you can judge this by simply looking at the rock. Does it have lots of different colors? Can you see which side of the rock was facing up and getting light in the ocean? Can you see sponges, coraline algae, and other good stuff growing on the rock? All of these are desirable and show there is a lot of good life on the rock.
Smell can be a great indicator of the condition of the live rock. Rock that is not cured will smell bad, it will smell like rotting garbage or bad eggs. Good rock won’t have a smell at all, or it will just smell like the beach. If the rock has any bad odor to it at all then it’s not cured (see below).
Aquacultured rock is more accurately called maricultured since it is grown in the ocean, not in aquariums. It is rock that was dry, was put out in the ocean for a few years, and then collected and sold. This can be great rock. Since it is placed in locations most likely to allow the most life to inhabit it there can be tons of great stuff on it. It does cost more though, as much as $15.00 per pound. However, I had a customer who bought some that was shipped submerged and it actually came in as the best rock I had ever seen (brain corals still alive on it) and it cost something like $8.00 shipped so it was a great deal.
Used rock (rock from other aquarists) can be good or bad. You may get a steal (someone with a nice reef tank who has to move and is selling everything) or you may get a dud (someone who neglected their tank and finally gave up). So take a good look at it before you buy anything from someone else’s tank. I have seen the best rock available like this, and I have seen stuff covered in hair algae, aiptasia, and not much else.
Fake Live Rock:
Be aware, there is fake live rock out there. You usually see it as dry rock painted to look live (gray with some fake pink and purple patches of ‘coralline algae’). However I am sure some shops have tossed it in their live rock tubs and sold it as live. Once you see a little live rock the fake stuff should stick out like a sore thumb.
Curing Live Rock:
Curing live rock is pretty simple and straight forward. Before adding any other livestock, simply add all the live rock you are going to and let it cure in the tank. Curing is the process of allowing anything that died during transport to decay. As the rock cures it will cycle the tank. If the live rock was cured when you bought it you should transport it home completely submerged to keep everything alive. If this is the case it may not need to cure at all and the tank will be instantly cycled, but you should still let it run a few days to make sure. Depending on how bad the rock is it may take a week to a few weeks for live rock to cycle. Just like cycling a freshwater tank you can test ammonia and nitrite daily. Once the nitrite is back down to 0ppm the tank is cycled. Then do a large water change or two to get the nitrate back down as low as possible and start stocking. Do not add ammonia. Once the rock is cured, the tank is cycled, and you do the water changes you can begin stocking.
Arranging Live Rock:
Stacking the rock seems simple, but many people get frustrated by it. Overall it is up to you what looks good. I prefer to keep as few pieces touching the sand as possible. This keeps more of the sand bed available for sifters like certain fish, snails, etc. It also keeps the flow higher around the bottom (less debris and food trapped and rotting). I also like to keep all the bottom pieces off the back of the tank. I don’t mind leaning some on the glass higher up the pile, but along the back of the bottom I want to be able to see (in case a fish is missing), as well as keep space for water flow. Flow all around the live rock is important for it to be able to provide filtration. I actually like to have a powerhead behind the rock shooting water across the back of the tank to keep debris moving for filter feeders to grab and keep flow all around and through the rock.
I don’t like to do anything permanent to the rock so I don’t use epoxy to stick it together. I have seen people use black zip ties to connect pieces to make them more stable, and even drill holes for the zip ties to fit in. In addition, some people will drill 1/2″ holes all the way through the rock and use 1/2″ acrylic rods through these holes to create some very nice arrangements. I think stacking is enough, but if you want something a little more intricate and customized, like a rock arch over open sand, then these options are perfect and easily undone if needed.
Make sure your largest fish have places to hide in the rocks. If you have large tangs or anything like that, make sure they have appropriately sized caves, you don’t want them trying to wedge themselves in to tiny crevices because they have no other options.