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Sand Beds

By Jonathan Lowrie. Presented June 14, 1998 on #reefs IRC.

Greetings folks. Thank you for joining in on the talk abut sand beds. I would like to begin by saying that I will probably deviate quite a bit from what most may be thinking this talk will be about.

I will NOT be discussing NNR systems, or plenums, and sand beds for filtration, etc. This material is commonly available all over in books, and on the net.  Frankly, there is little I could add, and I really don¹t subscribe to many of those thoughts anyhow, and shortly you will see why :-)

What I WILL discuss has to do with sand beds in nature. The reason why I feel this is critical to our success as aquarists, is that we try to duplicate a portion of nature in our tanks.  In order to successfully accomplish this feat, we must all understand better the processes involved. In order to best present this information, I would like to offer a few definitions of terms that I will be frequently referring to.

  • Infauna - Animals that live within sediments on seafloor bottom.
  • Epifauna - Benthic animals that crawl along the bottom or are firmly attached to bottom structures.
  • Macrofauna - Macroscopic animals that live on or in sediment.
  • Microfauna - Those animals less than 50 microns that live within The sediments.
  • Meiofauna - The animals between sizes. Also between spaces- these animals live within the interstitial spaces of the sediments.
  • Closed System - System which has no connection with outside environment. A typical home aquaria.
  • Open System - A system with a direct interchange with the outside environment.

So, I believe we are ready to begin. :-)

SeaFloor Characteristics

Seafloor characteristics are a crucial part of the habitat of benthic organisms. As the substrate supports the weight of many animals considerably more dense than seawater.   It also allows a place to construct burrows, tubes, or secure firm attachment to.

The seafloor also acts as a mechanical barrier to collect and accumulate plankton, waste material, and detritus. A variety of worms, echinoderms, mollusks, and crustaceans obtain their nourishment from this organic matter.

Benthic organisms are adapted for a particular bottom type; and character of life there, to a large extent, is dependent on the properties of bottom substrate. This bottom material varies from very solid rock to very soft, loose deposits.  The actual composition of the seafloor is determined principally by the amount of energy available. In nature this is through wind driven waves primarily.  In an aquarium, it can be from the use of auxiliary pumps.

Benthic animals play an important role in mixing and sorting of sediments by their burrowing and sorting of the sediments by their burrowing and feeding activities.   Oxygen and water from the sediment surface are transported down into the sediment through these tubes and burrows  Further modification of sedimentary characteristics is accomplished via cementing particles together to form tubes, and by compacting sediments together as fecal pellets and castings.

The distributional patterns of benthic animals and plants are strongly influenced by the form and texture of their substrate.  These factors determine effectiveness of locomotion, or for non motile species, the persistence of attachment to bottom.  So, what does all that mean for the home aquarium? I hope I have illustrated how important a role sediments of any type play in nature. It  provides nutrients, serves as a habitat.  It also acts as a source of minerals- more on this later. In our aquaria, it serves all these functions, plus adds a decorative flair to the overall appearance of the tank.

Animal Substrate Interaction

Because of the different distributions, unique adaptations have developed allowing for specialization to those environments.   The particle size and organic content of the bottom material limits the versatility; and thus the distribution of specialized feeding habits. 

Before you say Œhuh?¹, allow me to explain in terms of our captive closed systems. All the diverse habitat types in nature all support a selective array of animal life. What exists in one biotope, most probably will not exist in another. In our aquariums, this translates well into the discussion of live rock and live sand.

Live rock is a solid substrate. It has a variety of live within and about it. From small sponges, tunicates, to corals. Within may be alages, bacteria, and more. All of these animals and plants have adapted to life on a hard substrate such as the live rock. Sand on the other hand is a totally different environment.  It is much softer, and will not offer the same advantages to most of the animals

Yes, some will be able to make the transition, and tolerate the new habitat, but many will not migrate to the new habitat. Hence the reason why adding live rock to Œdead¹ sand will not ultimately lead to a live sand bed.

Before the critics jump up and yell, let me explain my opinion of live. Yes, the sand will have life in it. But will it have the typical life found within that format of sediment? No.  It has to come from somewhere, and sand animals and plants as a rule don¹t live on rock, and vie versa.

Suspension feeders depend on small plankton or detritus for nutrition.  Filtering devices or sticky mucous nets are employed to collect minute suspended food from the water. Suspension feeders generally require clean water to prevent accumulation of indigestible particles.

Deposit feeders engulf masses of sediments and process them through their digestive tract.  They extract nourishment through their digestive tract from the organic matter of the sediment in much the same manner as an earthworm.

If we are to keep obligate suspension feeders, or deposit feeders in our aquariums, we must be sure to provide them the proper and suitable habitat to thrive in.

To further discuss sediments I need to again clarify some vocabulary. Sediment size is discussed as the size of grains.  These range from boulder size Œgrains¹ that are greater than 256 millimeters, to silts and clays which are a minuscule 0.0004 millimeters.  Sands fall in the middle with coarse sand being 1 to 2 millimeters, and fine sands (oolitic sand) being 0.25 millimeters or smaller.

For a further discussion on sediment sizes, and types, please see June 1998 FAMA, and July 1998 FAMA for the article I co-authored with Eric Borneman.  It contains many relevant diagrams and charts that will allow a better understanding of today¹s chat.   This process is called sediment sorting.

Many reef sediments are terigenous in origin (in Atlantic reefs). Terrigenous sediments are those originating from terrestrial origins, and entering the ocean through streams and rivers.

The Atlantic Ocean has more large volume rivers that dump literally millions of cubic feet per hour of terrigenous sediments into the oceans.  Much of this falls along the Continental shelf, but some does reach the reef zones.

In the Pacific Ocean, there are less rivers with huge outflows, as well as deep trenches to collect and accumulate this sediment.

Another sediment type of reefs is biogenic sediment. Biogenic sediment is derived from living animal and plants.  These are sediments formed from diatoms skeletons, and skeletons of other animals and plants that have passed through the water column.   Biogenic sediments usually contain a high level of Calcium Carbonate.

I would like to share some of my personal research on reef habitats of the Atlantic Ocean.

I spent four years studying natural processes and the impact these had on reef systems of Florida and the Caribbean. Part of this was the in depth study of reef system sediments and nearby communities.

In a typical Florida reef, approximately 25% of the sediment is composed of crushed and broken coral skeletons. Acropora was the dominant skeleton found crushed along the reef base.

15% was calcareous algae. All the coralline encrusted bits and chunks of rock- thing GARF Grunge here :-)  30% was from the remnant of Halimeda skeletons. This is a calcareous macro alage that grows prolifically in Florida Reefs.  6% were from formaniferan skeletons and diatoms skeletons. Another 15% was composed of various mollusk shells.  Crushed oyster shells, clam shells and such.  The remaining 9% was miscellaneous debris that could not be classified and terrigenous mineral deposits.

In a Caribbean Reef 24% was coral skeletons, 33% was from coralline alages, 22% was from Halimeda alages, 12% was formaniferans, 8% was from mollusks, and the remainder unclassifiable.  What this appeared like was a coarse gravel with large chunks of coral skeleton that have a loose base of approximately 15 inches.  Beneath this was a porous hardpack of reef foundation material. This hard pack is cemented sediment that is usually quite porous in nature.

Nearby was an Inshore Boulder community. This is a shallow (4 to 6 meter) biotope that is characterized by smooth boulders and sand and hardpack rock.

This type of biotope has very little diversity, but was rather homogenous in its sediment composition. Further down the was the offshore boulder habitat.  It has a higher diversity with its 6 to 8 meter depth. It has more of the coral skeleton rubble. Its animal diversity was about 6% higher.  On the reef flat on the facing side is where I took the sediment measurements. On the leeward side, there was a considerable accumulation of sediments.

Many biogenic in nature. They were composed of remnants of biogenic films of cyanbacteria, seagrasses, and plankton.  It may be surprising to many that this very Œmud¹ like sediment was typical on the leeward channels of almost every reef flat visited.

Now, again, how does all this relate to the home aquarium? Coarse sediments are very difficult for animals to inhabit.  The sand grains are cutting, and have a considerable mass that can easily crush the soft bodied animals. Most life here tends to be tube burrowing worms, and mollusks.

Many are considered meiofauna as they exist in between sediment partakes as to prevent this destruction from abrasion.  Finer sediments from sandy silt to mud typically have a rich fauna. Thousands of species can be found in healthy sheltered mud flats and grass beds.  These natural sediment beds have another role as well. That role is as a mineral source.

In nature, marine sediments will sometimes release minerals that will precipitate to form irregular deposits on the seafloor.  In the global ocean these deposits generally have little impact on the chemistry. This nature of releasing minerals does play a role in a closed system.

Coral skeletons, and Halimeda is composed of calcium carbonate is composed of calcium carbonate in the form of aragonite.  While many of the red alages, and forams have CaCO3 in the form of calcite.

Without having awful chemistry lecture flashbacks, let me say that Calcium carbonate can exist in three forms- two of which are important to reef systems. Those are calcite and aragonite.

So now I am back to the nature of the sand bed of the home aquarium. Typically, folks dump in a uniform size gravel of aragonite based sand. As you can surmise, this is rather inadequate if you wish to support a large diversity of life within your sediment. This can be overcome in a variety of methods. The least effective- yet the easiest is to layer your sand in sizes.

Using a fine sand and a medium sand and a coarse sand you can replicate the diversity of sediments to a limited extent.  Many folk like to layer these is distinct layers, and even separate with screening.

I have found that overtime, energy from water flow, chemical processes, and any infaunal migration will thoroughly mix these layers. So, I have had great success dumping all my sediments into a container and mixing and adding to the tank. Next one will ask about depth.  Well, as I said, on a Caribbean reef the sand is loose to 15 to 20 inches.

Now since most of us don¹t want a sand tank with a few corals- we want a reef tank with some sand- what are we to do? I say at least 6 inches.  Go more if you can give up the space. There are many tricks to hide the substrate later to make the tank more aesthetically pleasing.  Another more complex method is to have a mixed sediment system.  This is involves using a sump and or refugium as well.

Rather than go into great detail and stir up controversies, I will say this: Refugia with seagrasses and mangroves serve many useful purposes. As a habitat for small shrimp, fish, mollusks, etc. And as a means to filter the aquarium. When I say filter- I also include mechanical and biological filtration.

Seagrasses in nature act as a baffle for sediment suspended in water, and will draw these sediments down to their bases.  In a properly flowing system the seagrasses can serve much the same purpose at home.

In a sump, you can also add a softer substrate to allow for the greater diversity of animals.  Wait! Someone is bound to ask why? Why do we want to increase diversity if our current NNR or other systems seem to work?

My initial reply usually involves a species list of what is in my systems...... animals like seapens, breeding Flame Scallops, and filterfeeding gorgonians. With the added diversity of animals and plants your system can better sustain your corals and fish.

A bit off the scope, this type of system will pave the way for going skimmerless. and heavy feedings. Both of which I recommend.

  To answer some of the many questions I see on the lists and message boards. Live sand will not form from dead sand.  Period.  Louis Pasteur proved the world wrong on spontaneous generation, and it wont happen in your reef tank. No matter how good the live rock is, it wont provide what is necessary for a healthy sand bed.

On shipping live sand.

As I said sand is rough Its cuts, it grinds. And have you ever lifted 50 pounds of it?!?  Imagine being a soft bodied annelid or a think shelled mollusk. And being grated, smashed, and smooshed by the sand.  And THEN handled by the airline luggage handlers or FEDEX !!!!!

Its a miracle any life makes it at all. In my opinion the shipment of living animals IN sand is a poor substitute at best.  Its best to collect them directly- not an option for many. So that leaves us with purchasing cultured animals that can populate sand beds. And a few outfits currently do this, and I hope more are developing this.

Well folks, that is about it. I hope I have broadened your outlook about what sand beds can do if applied properly. I will be happy to answer any involved questions via email at Thank you.


I wanted to know what the speaker thinks of collecting from the Salt Water Bays on the Gulf Coast... ah live sand and or animals?

I have collected from the Gulf Shore of Florida many times.  I have found the quality of infauna to be excellent for a reef system.  As for the sand, I suggest you sieve through it to separate the animals from the sediment, and transport separately.

Normally we buy live sand that is scooped up from the ocean floor around reefs. That sand is pretty homogeneous in particle size. Would our tanks be better off with a wider distribution of particle sizes?

In my opinoon, yes. Mixing of many particle sizes will allow for greater diversity to take place within sand bed.  This is quite easily done, as there are at least three grades of sand avaiable in most LFS.  Of course- you still have to 'seed' the proper animals to take advantage of this.

How is the live sand harvested and how is the natural reef impacted?

For research purposes I have collected live sand, in pint size bags, while keeping them completely underwater.  This allows for a segregation of layers- as I do not mix surface layers with bottom layers, etc.  But it is NOT commercially viable- as it took me hours to collect a mere 50 pounds of sand.  As for impact to reefs- new sand is formed daily from fish, inverts and waves.   I imagine it is minimal if done responsibly.

The cemented sediment, what is it "cemented with?... detritus? and how do we prevent it?

In nature- the cemented sediment was actual bonding of various ionic constituents. It was a beneficial aspect.  It acted liek a deep denitrification sponge beneath the sediment.  It does not have an analogous counterpart in a home system.  As for preventing it in a home system- I have never had to.   I keep a variety of fish and inverts that seem to keep the sand from becomming cemented. I have not done anything special to prevent this from ocurring.

What "sand sifting" animals are to be avoided in the reef tank?

My number one critter to avoid is the Horseshoe crab.  Awesome animals, just not suited for home use.  As for others- some of the more specific feeders. Many basket starts and crinoids due some excellent sediment sifting, but they are also very finicky about other habitat requirements.  I have a number of seapens that are amazing at mixing layers of sediments. They can dig down 10 inches in under 15 minutes, swell up and mix the sands. But they require a nearly continual dose of live foods.  So, I woudl say those animals that cannot be easily maintained because of size, diet of lifestyle.

"If you have a 48" deep aquarium would you try and put 15"+ of sand in it to replicate a reef enviorn.? If so are there any dangers of building toxic gases, etc.?"

Heeheehee. I have doen this- to some extent. I had a test tank that I was using to display the layering of sedimenta. It had wave action on top, and over time, you could see distinct layers of sediemnt based on size.   It was naturally collected sediment, although in the 'tank' portion, we kept no aninmals.  I never noticed any outgassing of significant nature. When we took the exhibit down, it has a slight odor to it.  Again- if its healtly it should naturally take care of all breakdown processes. This topic can be more fully covered via email. Just send me a note and I will be more than happy to provide more details.

If we use different layers of sand to diversify particle size, should screens be placed between the layers to prevent burrowing animals from churning and mixing the sand as you alluded to in your talk?

No- the mixing is good.

What do think the composition of a 6" sand bed should contain. ex, clay olithic sand coarse coral tc.?

Well, some % of oolitic sand, some 'fine' sand, and some crushed coral. Thsi is three grades that can be found at most LFS.  I would stay away from clays and silts and muds in MAIN tank. I have foudn they require a special sump to prevent them from stressing the organisms because of the fine particle size and the high energy levels in the tank. The suspended particles will cause corals to close up.

You've talked mainly about white sand Is Black Sand a viable thing for an aquarium?

I am not familar with the product you mean specifically.  Dyded black sand is NOT good.  As for natural black sand- as in volcanic ash, I would shy away from it from potential mineral release. I dont knwo for sure- but I suspct black sand could contain many undesirable compounds.

In a deep sand base how to we keep from developing dead spots, and how deep do you recommend?

In a home tank- 6 inches minimum. 8 to 10 if you can 'afford' the sapce. It DOES take away from water volume, so you have to make a choice.   Another option is to do 5 to 6 in tank, and have a sump with 10 inches.  As for dead spots- I dont do anything. I have not had them as a significant problem. They exist in nature and in tanks. With a healthly system, it should not be an issue.

What about all this talk about "MUD" filtration, usefull or hype?

Hmm. What 'type' of MUD filtration? The mud system as advertised to be used without a sand bed, and releys heavily on Calupera is IMO bunk.  I have tested this 'miracle mud' and its terrigenous sediment from the So Cal Mountains. So its not marine in origin, and as such has no special properties. I do feel that mud liek sediments are beneficial. And that is explained in great detail in June and July FAMA issues. PS- email me on that as well.

Do you think we have enough cultuered species so that we don't need natural live sand anymore?

NO!!!!!!!! SM I WISH we did.

Is there a reference we can look at to get addresses and phone #'s of suppliers?

I can make one up and have it posted on the website. I presume that is ok.

Less tna 6" of sand, say 2-3", worse than just a thin layer used for decrative effect?

Generally no. Even a small sand bed will have an important biologic function. It will not support a great diversity of infauna- but it will do some denitrification, as well as provide a habitat for small crustaceans, etc.

Since most of us cannot collect How can we get the "Live Sand" if the creatures are killed in shipping?

Short of separate shipment of animals colelcted from sand, I have no good answer.   Packaging of animals seprate of the sand will have the best odds of survival and you know what you are placing in tank.  That seems to be the best way at this point in time.  I have heard that some have developed better shipment methods, but have no experience with them.

If one adds more sand to their tank how should one do it?Remove all detrius?Mix it throughly?

Add it above existing sand. I prefer to leave detritus. Dont knwo why- just a thing I do.  DONT mix it. Allow the sediments to sort naturally.  Since that was brought up- I do NOT liek the idea of mixing sand once its in the tank.  I do mix sand sizes in a new system prior to adding to system.  But oince they are in the tank- allow natural processes (energy transfer and animals) to mix for you.

Is the live sand that we now purchase from our LFS of any real value?

I cannot say. At my LFS its worthless.  But there is SOME good live sand out there.

What in your opinion is the best place to get live sand? Mail order, lfs etc

Tough one to qualify.  LFS get it from mostly the same sources that mail order stores do. Some MO stores collect their own.  If you can get it with minimal handling- it will be better.  So, collecter to wholesaler to door os best. The more intermediate steps, the more time passes and the more damage.

Are commecially available sand bed boosters worth it?

I KNEW that was coming........ In clinical trials I found no difference in system susing 'vital' products and systems without.

Would collecting sand from local areas including non tropical areas be ok?

Yes and no. I have a tropical tank with many animals from Long Island Sound.  The more temeprate you go the more problems you will have.  Coller climate animals wont adapt well to tropical tank temps, and you run risk of introducing unwanted predatorsa etc.  But if you collected in summer, from local waters (legally or course) and set this up for culture.  You could then harvest works, clams, and crustaceans that come from it- without fear'of intriducing any contaminants.

Do you know of anyone that ships the animals separate from sand?

Yes, Inland Aquatics sells a detrivore kit that is useful for this purpose.  I believe the site has a catalog and more info on live sand critters for sale

When one adds sand to a new system.. do you recommend any commercial cycle products, grunge things etc?

I dont add any commercial products to any of my systems.  However for a new system- you must allow it to cycle. And it will cycle faster if you 'seed' it with material from an esta=blsuhed system.  I use my own GARF GRUNGE liek material- its just my own reef rubble from my ssytems. Same thing, more or less.  I would add the living animals to the system as soon as the rock is cured.

I think some wanted to know if "cycle helpers" actaually help?

Well, without starting a whole new chat.....  I have looked at BioZyme, FritzZyme, Cycle Vital....  And others.  NONE do what they claim on package. Some help. To some level. Lets leave it at that (for now).

What if anything can one look for in "good" live sand that cannot be found "bad" live sand?

Polychaets, and annelids. And small bivales. Liek Macomas (duck clams) or Gem shells.   Anything soft and crushable.  If those are present (and you most certainly WANT them) then you have excellent sand.
PS  Hopefully the larval forms of many of these will survive in your sand ansd grow up to populate it later.

Thanks Jonathan

Created by liquid
Last modified 2006-11-28 04:07