Flame Angel
New Member
I figured this might be a good thing to have in the forums, in case someone needed info on LR...and if we get a beginner's forum in the future, it can always be moved to there. It's an article written by James Fatherree for the October 2003 issue of Tropical Fish Hobbyist, which defines and explains live rock in detail.
ENORMOUSLY ANNOYING BOLD FONT: I DID NOT WRITE THIS ARTICLE, SO DON'T GIVE ME HELL IF YOU THINK I DID.
Anyway, on to the article...
Live rock is the ever-present structural foundation for essentially all reef aquariums, and it is also used by a large number of hobbyists in non-reef aquariums, as well. However, while it may seem to be everywhere in the marine aquarium hobby, many people literally know next to nothing about it, and few know lots about it. So, I'll run through some information on the subject, and maybe you'll pick up something from it.
What Exactly Is Live Rock?
For the most part, live rock is nothing more than limestone that has been collected from reef areas where loose rock rubble can be picked up. The erosive forces of wave activity can slowly break apart reef structures a little at a time, but the can also loosen and strip away large quantities of the reef's limestone framework during storms. Then these limestone chunks can be rolled around and further broken up, can be abraded by sand, can be worked over by various biting/boring/burrowing organisms, can be colonized by various others, and are also affected by water chemistry, all of which can dramatically change their appearances. The net result is that in certain environments these very diverse-looking, broken away pieces of limestone end up at rest on the surface and can be collected.
A wide variety of organisms can
show up when you add live rock to an
aquarium. This small piece came with a
limpet and a few nice sponges included.
These pieces of limestone that have been removed from reef structures typically have some sorts of reef organisms living in and on them, hence the name live rock. This may be only bacteria or coralline algae, but it can also be live corals at times, all of which may have been in or on a piece while it was still attached, or may have colonized it later. I'll explain more about that soon. The basic thing to keep in mind is that the limestone rock itself is no more alive than a hunk of limestone blasted out of a quarry wall in Indiana. It's all of the things that can be found living in and on such rocks that give them the name.
How Does Live Rock Form?
A wide variety of organisms in the marine realm use calcite and/or aragonite to form skeletal/structural material. Both of the minerals are composed of calcium carbonate, which organisms can produce by removing calcium from sea water and combining it with some carbon dioxide (of course it's much more complicated than that.) Organisms such as stony corals use this material to produce their skeletons, while clams and snails use it to build their shells. Numerous sorts of calcareous algae use it to strengthen their structures or to produce tough rinds on surfaces, and even a host of plankton use it to build miniscule containers for themselves.
Left: This piece of base rock clearly shows how porous some limestone can be.
This piece has been subjected to substantial boring by organisms and natural erosion,
as well. Right: Once in place, if you'll use calcium additions and maintain good water quality,
essentially all of your rock can become encrusted with colorful coralline algae.
When conditions are right, it can also precipitate directly from sea water without any biological help. Conversely, it can salso dissolve back into the sea water depending on environmental parameters such as carbon dioxide concentration and pH. And, because the ocean is such a dynamic environment, these sorts of back-and-forth reactions are occuring night and day on some scale within various sediments and rocks.
So, in a simplisitic sense, stony corals build skeletons, which accumulate and form the basic structure of a reef with the help of these other biologic and non-biologic activities. The corals make large skeletons, which are frequently broken up by storms and such, and are also overgrown by new growth. Simultaneously, other organisms produce a constant supply of bits and pieces to add in. Some produce large shells, while others produce a constant supply of tine calcium carbonate particles, such as when a dead calcaraeous algae is ground up by predators and waves. Then the whole mix is "glued" together by the runds formed by other calcareous algae and by non-biologic precipitation, and is also dissolved and eroded in other places at the same time. Thus, the net result is a reef structure made of a jumble of these pieces and calcium carbonate glue. This structure may also have a highly variable amount of pore/void space within it, which is also colonized by living reef organisms.
Quality aquacultured live rock often has nice live corals on it, and
many exceptional pieces are sold as "coral rock." This hardy
specimen has tripled in size in my tank.
Now, it's easy to get confused by all the names, but whether something composed of calcium carbonate was called calcite or aragonite, or was made by an organism or not, it can also be called limestone. In general, once a coral is dead, we can say the piece of skeleton left behind is literally nothing but a piece of limestone. We can say the same thing about the whole structure produced by a reef, as well. It is a large limestone structure, since it is composed of calcium carbonate. Limestone has also been formed under many conditions in a wide range of other marine environments in the past, and doesn't necessarily require corals to be involved, either.
Thus, a typical piece of live rock is basically just a chunk of limestone that has been broken away from a reef, and that had some life on it when it broke away or was colonized by things afterwards. Or, it can also be a piece of limestone that broke away from a much older geologic formationon the seafloor that has been subsequently colonized. Either way, it's limestone with stuff on it, and if you break a piece in half it can be quite obvious at times. Typically what you'll see is exactly what you'd expect given this information on how it forms: chunks of coral skeleton, bits and pieces of shells and such, and a lot of limestone glue holding it together.
In addition, live rock can also be produced by taking rock from the land and dumping it in the ocean in an appropriate location, then just waiting for it become colonized. This is called live rock aquaculture, and businesses simply use quarried limestone pieces from areas that were submerged in the past. So, even though they're just plain limestone rocks in a pit now, those same pieces were formed by marine organisms and processes in the geologic past; the sea level has just gone down and exposed them. Once quarried, these pieces of ancient seafloor are carried out on boats and barges, dumped in predetermined areas, and then left for some time where the piles of rock can act as small man-made reef structues. Eventually they are then colonized by the same sorts of things would be found on a natural reef, and they can be collected and sold.
Where Does Live Rock Come From?
Live rock is collected in a number of places, although the availability list has changed a good bit from time to time. Many years ago, almost all of it came from Florida waters and was relatively cheap. Live rock has also been coming from a few Pacific areas, but it was far less popular; the cost and the freight charges from so far away were substantially higher, making it less profitable for stores.
It is easy to see that not all pices of live rock look
like rocks. These pices of Tonga branch that I
bleached are obviously pices of staghorn corals that have
been broken up and partially covered over by coralline
algal rinds.
Then the collection of "wild" live rock in U.S. waters was banned by the government in January of 1997, and there was no alternative to the higher prices of the Pacific stuff. Live rock started coming from a wide variety of places, including some you've probably heard of, such as Fiji, Tonga, and Samoa, filling the gap in the market. Most of these areas are still shipping today, but the aquacultured live rock business in Florida got going, too. Now the aquacultured live rock produced in the Gulf of Mexico and the Florida Keys has made its way into the market with the Pacific rock, the result being a variety of live rock from a variety of areas to choose from, with the interesting thing being that they are all a little different.
What Kind of Stuff Is On Live Rock?
That's a big question! With collected rock, you may find basically nothing on it, or you may find some of just about everything, depending on where it was collected and what type of rock it is. In general you can expect a significanty variety of microorganisms to be populating any given pice of live rock. Most most live rock will also show at least some coverage by coralline algae, typically giving it a patchy purple, pink, and/or red appearance. But that's about it for a large part of what you'll see for sale.
Large rocks quarried in Florida and used in
aquaculture are often more dense than others, but it
is still easy to see that they are nothing but pieces of
corals, shells, and such, all melded together.
On the other end of the spectrum, top-quality aquacultured rock often has an impressive variety of life on it. The microorganisms are there of course, but there may also be a variety of macroalgae, sponges, tunicates, bryozoans, worms, clams, snails, crabs, hermit crabs, shrimps, barnacles, brittle stars, sea stars, urchins, anemones, and soft and stony corals, etc. - lots of stuff!
This absence or abundance of life is related to a number of factors, but it is primarily the age of the rock and how long it has been exposed. Obviously, if a rock has been buried in sand, or was sandblasted and rolled around during a relatively recent storm, you won't find too many of these things living on it. Conversely, if a rock has been exposed for years and has not been subjected to abusive storm activity, many things will have time to colonize it and call it home. In a way, each piece can become its owwn micro-reef ecosystem if given enough time.
What Is The Best Type(s) of Live Rock?
That's a tough one because, as I said, there are a variety of types from a variety of places, and I can't really say one particularly type is perfect for all occasions. For example, "Tonga branch" live rock looks just like the name sounds. It is really just broken up pieces of staghorn coral that have died, been "worked on," and have been overgrown by coralline algae. Thus, it has a very distinctive form and doesn't really look like a rock at all. You could use it to build a whole reef structure in yor tank, but many hobbyists prefer to just use a piece here and there for decoration with some other type of rock making the base structure.
Aquacultured live rock typically has the most live stuff on it, but if you are bulding a stacked-up structure, much of it would be killed or would slowly die off after being covered up. Conversely, much of the other Pacific rock has very little life on it, but often comes in especially interesting shapes, and is relatively lightweight. It might not be "alive" enough for you to build your whole structure with, but some pieces are so neat looking that they make great additions.
What you do want to keep in mind when trying to choose is that none of it is cheap, and while you'll want to make your tank look the way you want, you will probably also want to use the least amount of live rock to do it. Most Pacific rock is relatively porous and lightweight and has lots of open shapes. Thus, you can use fewer pounds (it's sold by the pound) to take up more room in a tank. If stacked right, just a few big pieces can really take up a lot of room and look great. Conversely, Florida rock tends to be less porous and can be relatively heavy, so it would take more pounds to fill the same amount of space. But Florida rock typically has so much more life on it compared to Pacific rock that it may be worth the extra cost to you.
With that being said, I should also throw in a bit about base rock. Base rock is basically live rock with nothing on it, and it may even be sold dry. It is also limestone rubble, but it generally has nothing living on it with the possible exception of some microorganisms. This means it's much cheaper, and can be used to build the base of the structure in an aquarium, with the real live rock going on top. So your best bet may be mixing them - using a few pieces of top-quality Florida and/or Pacific rock on top of the base rock structure you build, and maybe even throwing in some of the branch-type rock, too.
As a last note on this topic, if possible, you should also consider using aquacultured live rock and/or base rock for environmentally friendly reasons, as it reduces the impact of live rock collection in natural marine environments elsewhere. I'll also add that it is the way to go if you plan on having a deep sand bed setup in a reef tank, as it tends to carry a much greater diversity and abundance of the sorts of critters you'll want to introduce into your substrate.
Does it Require Any Special Care?
When live rock comes in, it can and almost always will go through a period of die off (of the critters, not the rock itself). I've picked up boxes of rock at the airport that stunk so badly I had to hold my breath while carrying them, which was always a sure sign of lots of dead, rotting clams. It had arrived about 48 hours later than scheduled and everything on it had croaked. So, bad things can happen to live rock.
At times, hobbyists use separate containers to "cure" live rock before
adding it to an aquarium. However, this should only be required if there
is a substantial die off of organisms on the rock, which would really foul
up the water quality in the aquarium.
Even live rock that has been treated fairly well and shipped quickly will still often experience some die off of whatever is living on it, so you do have to watch out. Obviously the stinking dead clam rock couldn't be put in an aquarium, but you'll need to be cautious of rock even if it only has a mild stink to it. If you add too much at one time, with too much odor, you'll be asking for trouble, as you may overload your system with decay-produced ammonia.
Some people used to "cure" rock first to avoid any such problems. This basically meant keeping it in a separate, unlit tank until everything on it that could die did and wasted away. But this often seemed to lead to the production of expensive base rock. So most people don't cure live rock unless it is in really bad shape, like my deam-clam rock. You'll just have to make a judgement call on what to do should you find yourself in such a situation, as it could be possible to add smelly rock to an aquarium and do water changes until the stinking stops in an effort to save whatever else may still be alive on it. Going over each piece and hand-removing anything dead or dying beforehand will be essential, of course.
Other than that, once it's in a tank you'll want to use calcium additions to keep the calcareous coralline algae growing and help it spread from covered areas to bare areas. Like corals and all the other calcium carbonate precipitating specimens, it requires an adequate concentration of calcium in the waterand good water quality, too. If that is provided, given enough time, live rock can become completely encrusted and look absolutely beautiful.
Are There Things to Watch Out For?
As a word of precation, I'd be wary of buying a large quantity of live rock at one time from a mail order/online supplier unless they are very reputable (some are, many aren't). Instead, you may want to buy a "sample" shipment to check out, then order more. Because shipments can be delayed or subjected to detrimental temperature extremes, if you are buying a lot you may want to get a few separate shipments anyway. That way if anything goes wrong it may only get some of your rock and not all of it. Of course, this really depends on your own situation and needs, and doesn't apply to purchases made at local shops.
And one last note: Whether you are buying at a shop or somewhere else, don't buy all small pieces! Buy big pieces, as they are far easier to arrange in ways that take up the most amount of space per pound used. If you buy 100 potato-sized pieces, you'll likely end up with a pile of live rock in your aquarium that resembles a pile of 100 potatoes.
ENORMOUSLY ANNOYING BOLD FONT: I DID NOT WRITE THIS ARTICLE, SO DON'T GIVE ME HELL IF YOU THINK I DID.
Anyway, on to the article...
Live rock is the ever-present structural foundation for essentially all reef aquariums, and it is also used by a large number of hobbyists in non-reef aquariums, as well. However, while it may seem to be everywhere in the marine aquarium hobby, many people literally know next to nothing about it, and few know lots about it. So, I'll run through some information on the subject, and maybe you'll pick up something from it.
What Exactly Is Live Rock?
For the most part, live rock is nothing more than limestone that has been collected from reef areas where loose rock rubble can be picked up. The erosive forces of wave activity can slowly break apart reef structures a little at a time, but the can also loosen and strip away large quantities of the reef's limestone framework during storms. Then these limestone chunks can be rolled around and further broken up, can be abraded by sand, can be worked over by various biting/boring/burrowing organisms, can be colonized by various others, and are also affected by water chemistry, all of which can dramatically change their appearances. The net result is that in certain environments these very diverse-looking, broken away pieces of limestone end up at rest on the surface and can be collected.
A wide variety of organisms can
show up when you add live rock to an
aquarium. This small piece came with a
limpet and a few nice sponges included.
These pieces of limestone that have been removed from reef structures typically have some sorts of reef organisms living in and on them, hence the name live rock. This may be only bacteria or coralline algae, but it can also be live corals at times, all of which may have been in or on a piece while it was still attached, or may have colonized it later. I'll explain more about that soon. The basic thing to keep in mind is that the limestone rock itself is no more alive than a hunk of limestone blasted out of a quarry wall in Indiana. It's all of the things that can be found living in and on such rocks that give them the name.
How Does Live Rock Form?
A wide variety of organisms in the marine realm use calcite and/or aragonite to form skeletal/structural material. Both of the minerals are composed of calcium carbonate, which organisms can produce by removing calcium from sea water and combining it with some carbon dioxide (of course it's much more complicated than that.) Organisms such as stony corals use this material to produce their skeletons, while clams and snails use it to build their shells. Numerous sorts of calcareous algae use it to strengthen their structures or to produce tough rinds on surfaces, and even a host of plankton use it to build miniscule containers for themselves.
Left: This piece of base rock clearly shows how porous some limestone can be.
This piece has been subjected to substantial boring by organisms and natural erosion,
as well. Right: Once in place, if you'll use calcium additions and maintain good water quality,
essentially all of your rock can become encrusted with colorful coralline algae.
When conditions are right, it can also precipitate directly from sea water without any biological help. Conversely, it can salso dissolve back into the sea water depending on environmental parameters such as carbon dioxide concentration and pH. And, because the ocean is such a dynamic environment, these sorts of back-and-forth reactions are occuring night and day on some scale within various sediments and rocks.
So, in a simplisitic sense, stony corals build skeletons, which accumulate and form the basic structure of a reef with the help of these other biologic and non-biologic activities. The corals make large skeletons, which are frequently broken up by storms and such, and are also overgrown by new growth. Simultaneously, other organisms produce a constant supply of bits and pieces to add in. Some produce large shells, while others produce a constant supply of tine calcium carbonate particles, such as when a dead calcaraeous algae is ground up by predators and waves. Then the whole mix is "glued" together by the runds formed by other calcareous algae and by non-biologic precipitation, and is also dissolved and eroded in other places at the same time. Thus, the net result is a reef structure made of a jumble of these pieces and calcium carbonate glue. This structure may also have a highly variable amount of pore/void space within it, which is also colonized by living reef organisms.
Quality aquacultured live rock often has nice live corals on it, and
many exceptional pieces are sold as "coral rock." This hardy
specimen has tripled in size in my tank.
Now, it's easy to get confused by all the names, but whether something composed of calcium carbonate was called calcite or aragonite, or was made by an organism or not, it can also be called limestone. In general, once a coral is dead, we can say the piece of skeleton left behind is literally nothing but a piece of limestone. We can say the same thing about the whole structure produced by a reef, as well. It is a large limestone structure, since it is composed of calcium carbonate. Limestone has also been formed under many conditions in a wide range of other marine environments in the past, and doesn't necessarily require corals to be involved, either.
Thus, a typical piece of live rock is basically just a chunk of limestone that has been broken away from a reef, and that had some life on it when it broke away or was colonized by things afterwards. Or, it can also be a piece of limestone that broke away from a much older geologic formationon the seafloor that has been subsequently colonized. Either way, it's limestone with stuff on it, and if you break a piece in half it can be quite obvious at times. Typically what you'll see is exactly what you'd expect given this information on how it forms: chunks of coral skeleton, bits and pieces of shells and such, and a lot of limestone glue holding it together.
In addition, live rock can also be produced by taking rock from the land and dumping it in the ocean in an appropriate location, then just waiting for it become colonized. This is called live rock aquaculture, and businesses simply use quarried limestone pieces from areas that were submerged in the past. So, even though they're just plain limestone rocks in a pit now, those same pieces were formed by marine organisms and processes in the geologic past; the sea level has just gone down and exposed them. Once quarried, these pieces of ancient seafloor are carried out on boats and barges, dumped in predetermined areas, and then left for some time where the piles of rock can act as small man-made reef structues. Eventually they are then colonized by the same sorts of things would be found on a natural reef, and they can be collected and sold.
Where Does Live Rock Come From?
Live rock is collected in a number of places, although the availability list has changed a good bit from time to time. Many years ago, almost all of it came from Florida waters and was relatively cheap. Live rock has also been coming from a few Pacific areas, but it was far less popular; the cost and the freight charges from so far away were substantially higher, making it less profitable for stores.
It is easy to see that not all pices of live rock look
like rocks. These pices of Tonga branch that I
bleached are obviously pices of staghorn corals that have
been broken up and partially covered over by coralline
algal rinds.
Then the collection of "wild" live rock in U.S. waters was banned by the government in January of 1997, and there was no alternative to the higher prices of the Pacific stuff. Live rock started coming from a wide variety of places, including some you've probably heard of, such as Fiji, Tonga, and Samoa, filling the gap in the market. Most of these areas are still shipping today, but the aquacultured live rock business in Florida got going, too. Now the aquacultured live rock produced in the Gulf of Mexico and the Florida Keys has made its way into the market with the Pacific rock, the result being a variety of live rock from a variety of areas to choose from, with the interesting thing being that they are all a little different.
What Kind of Stuff Is On Live Rock?
That's a big question! With collected rock, you may find basically nothing on it, or you may find some of just about everything, depending on where it was collected and what type of rock it is. In general you can expect a significanty variety of microorganisms to be populating any given pice of live rock. Most most live rock will also show at least some coverage by coralline algae, typically giving it a patchy purple, pink, and/or red appearance. But that's about it for a large part of what you'll see for sale.
Large rocks quarried in Florida and used in
aquaculture are often more dense than others, but it
is still easy to see that they are nothing but pieces of
corals, shells, and such, all melded together.
On the other end of the spectrum, top-quality aquacultured rock often has an impressive variety of life on it. The microorganisms are there of course, but there may also be a variety of macroalgae, sponges, tunicates, bryozoans, worms, clams, snails, crabs, hermit crabs, shrimps, barnacles, brittle stars, sea stars, urchins, anemones, and soft and stony corals, etc. - lots of stuff!
This absence or abundance of life is related to a number of factors, but it is primarily the age of the rock and how long it has been exposed. Obviously, if a rock has been buried in sand, or was sandblasted and rolled around during a relatively recent storm, you won't find too many of these things living on it. Conversely, if a rock has been exposed for years and has not been subjected to abusive storm activity, many things will have time to colonize it and call it home. In a way, each piece can become its owwn micro-reef ecosystem if given enough time.
What Is The Best Type(s) of Live Rock?
That's a tough one because, as I said, there are a variety of types from a variety of places, and I can't really say one particularly type is perfect for all occasions. For example, "Tonga branch" live rock looks just like the name sounds. It is really just broken up pieces of staghorn coral that have died, been "worked on," and have been overgrown by coralline algae. Thus, it has a very distinctive form and doesn't really look like a rock at all. You could use it to build a whole reef structure in yor tank, but many hobbyists prefer to just use a piece here and there for decoration with some other type of rock making the base structure.
Aquacultured live rock typically has the most live stuff on it, but if you are bulding a stacked-up structure, much of it would be killed or would slowly die off after being covered up. Conversely, much of the other Pacific rock has very little life on it, but often comes in especially interesting shapes, and is relatively lightweight. It might not be "alive" enough for you to build your whole structure with, but some pieces are so neat looking that they make great additions.
What you do want to keep in mind when trying to choose is that none of it is cheap, and while you'll want to make your tank look the way you want, you will probably also want to use the least amount of live rock to do it. Most Pacific rock is relatively porous and lightweight and has lots of open shapes. Thus, you can use fewer pounds (it's sold by the pound) to take up more room in a tank. If stacked right, just a few big pieces can really take up a lot of room and look great. Conversely, Florida rock tends to be less porous and can be relatively heavy, so it would take more pounds to fill the same amount of space. But Florida rock typically has so much more life on it compared to Pacific rock that it may be worth the extra cost to you.
With that being said, I should also throw in a bit about base rock. Base rock is basically live rock with nothing on it, and it may even be sold dry. It is also limestone rubble, but it generally has nothing living on it with the possible exception of some microorganisms. This means it's much cheaper, and can be used to build the base of the structure in an aquarium, with the real live rock going on top. So your best bet may be mixing them - using a few pieces of top-quality Florida and/or Pacific rock on top of the base rock structure you build, and maybe even throwing in some of the branch-type rock, too.
As a last note on this topic, if possible, you should also consider using aquacultured live rock and/or base rock for environmentally friendly reasons, as it reduces the impact of live rock collection in natural marine environments elsewhere. I'll also add that it is the way to go if you plan on having a deep sand bed setup in a reef tank, as it tends to carry a much greater diversity and abundance of the sorts of critters you'll want to introduce into your substrate.
Does it Require Any Special Care?
When live rock comes in, it can and almost always will go through a period of die off (of the critters, not the rock itself). I've picked up boxes of rock at the airport that stunk so badly I had to hold my breath while carrying them, which was always a sure sign of lots of dead, rotting clams. It had arrived about 48 hours later than scheduled and everything on it had croaked. So, bad things can happen to live rock.
At times, hobbyists use separate containers to "cure" live rock before
adding it to an aquarium. However, this should only be required if there
is a substantial die off of organisms on the rock, which would really foul
up the water quality in the aquarium.
Even live rock that has been treated fairly well and shipped quickly will still often experience some die off of whatever is living on it, so you do have to watch out. Obviously the stinking dead clam rock couldn't be put in an aquarium, but you'll need to be cautious of rock even if it only has a mild stink to it. If you add too much at one time, with too much odor, you'll be asking for trouble, as you may overload your system with decay-produced ammonia.
Some people used to "cure" rock first to avoid any such problems. This basically meant keeping it in a separate, unlit tank until everything on it that could die did and wasted away. But this often seemed to lead to the production of expensive base rock. So most people don't cure live rock unless it is in really bad shape, like my deam-clam rock. You'll just have to make a judgement call on what to do should you find yourself in such a situation, as it could be possible to add smelly rock to an aquarium and do water changes until the stinking stops in an effort to save whatever else may still be alive on it. Going over each piece and hand-removing anything dead or dying beforehand will be essential, of course.
Other than that, once it's in a tank you'll want to use calcium additions to keep the calcareous coralline algae growing and help it spread from covered areas to bare areas. Like corals and all the other calcium carbonate precipitating specimens, it requires an adequate concentration of calcium in the waterand good water quality, too. If that is provided, given enough time, live rock can become completely encrusted and look absolutely beautiful.
Are There Things to Watch Out For?
As a word of precation, I'd be wary of buying a large quantity of live rock at one time from a mail order/online supplier unless they are very reputable (some are, many aren't). Instead, you may want to buy a "sample" shipment to check out, then order more. Because shipments can be delayed or subjected to detrimental temperature extremes, if you are buying a lot you may want to get a few separate shipments anyway. That way if anything goes wrong it may only get some of your rock and not all of it. Of course, this really depends on your own situation and needs, and doesn't apply to purchases made at local shops.
And one last note: Whether you are buying at a shop or somewhere else, don't buy all small pieces! Buy big pieces, as they are far easier to arrange in ways that take up the most amount of space per pound used. If you buy 100 potato-sized pieces, you'll likely end up with a pile of live rock in your aquarium that resembles a pile of 100 potatoes.
