Live Rock
Live rock is one of the best natural methods for filtration. When collected from the ocean, it usually consists of dead stony corals that have eroded and have turned into interesting forms and structures.

Live rock should be very porous and colonized with both nitrifying and denitrifying bacteria. These bacteria allow the rock to act as a complete biological filter. The nitrifying and denitrifying bacteria break down waste completely. With live rock there is no chance of a dangerous hydrogen sulfide build up.

Live rock can be visually appealing and can provide food for the other animals in the reef. Many times it comes with macro algae growing on the surface. If collected and shipped correctly it should arrive loaded with life.

Since the cost of shipping by air is great, live rock is usually shipped either dry or wrapped in moist newspaper. Many collectors power wash the newly collected live rock with seawater to remove much of the life forms attached like sponges. The reason for this, is to remove the life that will die due to the method of shipping. The rock is then “Cured” under a saltwater sprinkler system until it ships

Others will have it shipped direct from the ocean to their holding tanks where they cure it themselves. The theory behind this is that there will be more life on the rock when it arrives at the wholesaler/retailer.

Cured Live Rock

Rock that is sold as “Cured” live rock has been through a curing process and is supposedly ready to be placed into the reef aquarium on arrival. It should have a "Clean" ocean like smell to it and no dead or dying life should be found. Cured live rock will usually cost more than uncured but the benefit is, it can be placed in the tank immediately. Many times, mail order shipments can be delayed due to airline problems. Always check the shipment before placing it into an aquarium, as the "Cured" rock could have become "Uncured" rock due to the sitting on the tarmac in Minneapolis.

Uncured

Uncured rock has not been through a curing process or has been poorly shipped. This rock will have dead and dying sponges, anemones etc. on it and will be decomposing. There will be an odor ranging from mild decay to a strong ammonia smell.

Uncured Live rock is usually much cheaper than cured live rock. This is due to the fact that the retailer has not spent time, space and money curing the rock themselves.

One time I was at a buddy's and he had received a shipment of supposedly “Cured” live rock that had been delayed in Minneapolis on a hot day in the middle of the summer. We are pretty sure it had spent a lot of hours on the tarmac under the hot sun. When we opened the box, the odor of ammonia was so strong it burned our eyes and nose.

Checking/Curing Live Rock

There is a very simple and safe method for checking/curing live rock to tell when it is ready to be placed in your tank.

1. Before the rock is scheduled to arrive, make enough fresh saltwater to cover the rock in a clean trashcan. This water should be the same temperature and salinity as your tank water.

2. When the rock arrives, check it closely for and dead or decomposing animals and remove them if found.

3. Place the rock in a clean trashcan and cover it with the freshly made saltwater. I have a “Reef Only” trashcan that is only used for holding reef related items like water, rock, etc.

4. Place a power head or air stone in the can to circulate and oxygenate the water.

5. Maintain the temperature between 75 – 84 degrees F. and specific gravity between a specific gravity of 1.023 to1.027. Ideally you should maintain both at the same levels as your tank.

6. Test the water daily for Ammonia and Nitrite. After the ammonia and nitrite spikes peak and return to being undetectable, the rock is ready to place into your tank.
It usually takes 2 to 4 days for the ammonia readings to spike if there is decomposing like on the rock. If there is no spike after 4 days, and the ammonia/nitrite levels are undetectable, your rock should be ready to put into your tank.

If there is a spike of ammonia, there will be a spike of nitrite following it. Typically the ammonia/nitrite cycle will last 18 days.

Aquacultured Live rock

Aquacultured live rock is simply rock that has been placed in the ocean or man-made reef, and after a few years, becomes colonized with life just like live rock from the reef. The “Base Rock” can come from many different sources. In Florida, it is common to mine limestone and place it in the ocean where it can be “Seeded”.

Some retailers make their own rock using aragonite and Portland cement. The advantage to this is they can make and sizes more suitable to reef aquariums.

Man-made Live rock

A common practice is to make rock out of aragonite and Portland cement. This rock is easy to make and can make a very attractive reef. My personal tank is mostly made up of man-made rock that has never been in the ocean.

This rock should be made to be very porous to allow bacteria colonization through out the rock. Water will run through the rock I make, when held under a water faucet. The rock should also be made of reef compatible materials such as aragonite, crushed coral, crushed limestone etc. I have heard of some hobbyists using oyster shells sold at feed stores for making rock. I would not recommend this as oysters are not usually found on the reef, their shells are very dirty and undesirable elements could possibly leach into to your system

Once the rock has been created into the shapes desired, it must be cured for a period of at least 28 days. The cement that is used to make the rock has a very high pH level until it has cured and could cause a pH spike n your tank if placed in it too early.

Base Rock

Base rock is basically any rock that has no life on it. Aquacultured live rock started out as base rock. There are many different kinds of suitable base rock which can usually be purchased at a local fish store. Attributes of good base rock include the following.

1. Should be very porous to allow colonization of denitrifying bacteria deep within the rock. A concrete building block could be used as a base rock but since it is solid there would be very little life within.

2. Reef compatible. Many types of rock are not always compatible with reefs. Within a few miles of my house, there are many tons of lava rock that can be your for the taking. Many of these lave rocks are known to be unsuitable for a reef tank due to the high metal content.

3. Should be of shapes and sized that suit the aquascaping you want for your reef.
Making Rock “Live”

Neither base nor man-made rock will have life on it to start with. It will need to be “seeded” to start it on the way to becoming “live”. A couple of common methods to seeding the rock is to place it into a tank that contains live rock. The life from the live rock will eventually migrate to the man-made rock.

Another method is to spread live sand onto the rock. The bacteria and fauna in the sand will help colonize the rock causing it to become live after time.

A word of caution, ensure there are other means of biological filtration when using base/man-made rock. It takes many months before this rock will perform any noticeable filtration.