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Deep Sand Bed -- Anatomy & Terminology


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#1
Whys

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A deep sand bed, or DSB for short, can be a useful addition to a saltwater aquarium, refugium, or even a remote bin. Tho based on a remarkably simple idea, DSB discussions can become enormously complex. The purpose of this article is to offer a generalized understanding of the core concepts and specific terminology. This is by no means the final word on the DSB, nor does it advocate anything more than educating the reader, but it can also serve as a guide to a more serious investigation.

There are several potential benefits and possible drawbacks to having a DSB. Most often their purpose is for nitrate reduction, so that is this article's focus, but that is not their only purpose, nor is a DSB the only means for achieving that goal. Not everyone uses a DSB and many have tried them with poor results. Some do use a DSB and have reported good results for a decade or more. There is substantial disagreement as to why some succeed and others fail. Over the years, some general rules of thumb have evolved, but they should not be mistaken for definitive science. It is up to the reader to reach their own conclusions.

To better understand the anatomy of a deep sand bed, let us first look at a shallow sand bed, or SSB for short.

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- Oxic: oxygenated.
- Aerobic: requires oxygen to function.
- Nitrifying: converts ammonia into nitrate.


In all aquariums, decomposition is largely performed by bacteria, but the process can be facilitated by the presence of a "clean up crew", or CUC for short. Detritus (waste) and other organic matter is first eaten by the CUC of crabs, stars, hermits, and snails. The smaller particulates they produce are then further broken down by copepods, other benthic organisms, and worms. The remaining dissolved organics are then converted by the "nitrifying" bacteria, from ammonia (toxic), to nitrite (less toxic), to nitrate (least toxic). All of this takes place within a layer of sand oxygenated by moving water, termed oxic, and the bacteria there require oxygen to function, termed aerobic. In a shallow sand bed this is where the process ends. The nitrate simply accumulates in the water column to be removed by ritual water change.

In a deep sand bed, there are another type of bacteria, termed anaerobic, that require a depleted oxygen environment to function. Among these are the "denitrifying" bacteria that convert toxic nitrate into nitrogen (which is mostly inert). The primary objective of a DSB is to provide a layer of very low oxygen, termed hypoxic, where bacteria can function anaerobically. The potential harm is in creating a layer completely devoid of oxygen, termed anoxic, where "reducing" bacteria can convert sulfate into hydrogen sulfide (rotten egg smell). This and other toxins can dangerously accumulate in a sand bed that is too deep or not properly maintained.

The prevailing wisdom is that the worms and benthic organisms are vital to maintaining a healthy DSB. In addition to cleaning the sand, it is believed their gentle agitation of the bed helps deliver nutrients to the bacteria while preventing truly anoxic conditions.

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- Benthic: surface and near sub-surface sand bed layer.
- Hypoxic: low oxygen.
- Anoxic: no oxygen.
- Anaerobic: requires depleted oxygen to function.
- Denitrifying: converts nitrate into nitrogen.


The full benefits and challenges surrounding deep sand beds are still a matter of some debate, so it is important to point out that the conversation is often confused by competing terminology. Environmental scientists often borrow the term anoxic (labeled in blue) to mean extremely hypoxic, and anaerobic (labeled in blue) to mean truly anoxic.

Here are some general rules of thumb for maintaining a DSB. It should be at least four inches deep but no more than six, consisting mostly of fine grains, sometimes called "oolite" or "sugar-fine". Keep the benthic and worm populations healthy by avoiding Sand-Sifting stars, most crabs, and limiting hermits. Occasionally rejuvenate these populations with fresh liverock or true livesand from a well established aquarium, as this may be key to long term success. The sand bed should only be disrupted very gently over time. Brittle and baby stars, as well as Nassarius and Cerith snails, provide a slow and beneficial agitation of the sand, but vacuuming should be performed with great care, if performed at all. Remember, a deep sand bed is a living thing that must be kept in careful balance.

General Rules of Thumb:
- 4" to 6"; fine-grain; do not disturb or disturb with care.
- Helpful: Brittle & baby stars, Nassarius & Cerith snails.
- Unhelpful: Sand-Sifting stars, most crabs, too many hermits.
- Rejuvenate benthic and worm populations for long term success.



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(Jun,2009) Author & Illustrator: Whys. The following credits, listed in alphabetical order, are for collaborative work only and should not be assumed as endorsements of this article. Technical contributions: capn_hylinur, fsn77, jenglish, MattL, tmz, WaterKeeper. Additional peer review: adtravels, Biologist, luther1200, jasonrp104, Nanook, rishma, Sisterlimonpot, thegrun, therealfatman.


I've placed "Nitrifying", "Denitrifying" (or "Facultative"), and "Reducing" in quotes, because I believe these are the best words to use in order to prevent misunderstanding when discussing the DSB.

Hope this helps. :)

Edited by Whys, 29 February 2012 - 11:33 PM.


#2
C.I._Reefer

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wow, you wrote this 3 years ago?

#3
Whys

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Yes, but I've only just posted it here today. Credits have been given, but the names belong to another site.

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#4
C.I._Reefer

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Yes, but I've only just posted it here today. Credits have been given, but the names belong to another site.


nice write up... probably deserves a sticky. do you run a DSB personally?

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NancyC

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Thanks!

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Whys

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...do you run a DSB personally?


5 inches of OceanDirect Original Grade. It appears more colorful today, but here it was when it was first started.

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It has an eggcrate shelf to prevent rock work collapse due to shifting sand.

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I guess it must be about 4 years old now. I'll post a current picture when I have a chance.

I really enjoy having a DSB. I've never vacuumed the sand bed. Not once. An army of carefully cultivated Spionid worms keeps the sand bed clean...

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...and nitrates have never been detected.

Great for burrowing fish and inverts, or for sticking a coral upright in the sand. :)

Incidentally, Peppermint Shrimp will eat Spionid worms like spegetti! :/

Edited by Whys, 02 March 2012 - 01:49 PM.

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#7
Veng

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Looks awesome. I have to ask, that's not a metal bolt on those standoffs is it?

#8
Whys

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If you mean the legs under the eggcrate shelf, thats black PVC filled with silicone to prevent the trapping of detritus.

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#9
kgoldy

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Hey Whys, can you tell us a little more about your system, and your maintenance schedule?

I'm a DSB guy- running a year old tank that's had only 1 water change (back on July 4th). No skimmer, no filter socks, no GFO, no carbon... DSB and macro does it all.

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NancyC

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I'm sold, well as much as I can be in this ever changing world, on the DSB. I'll be setting up my new tank shortly. I get the eggcrate to keep the rock from shifting, but why does it need to be elevated? I'm not good with things like tools and measuring and cutting.

#11
Whys

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Hey Whys, can you tell us a little more about your system, and your maintenance schedule?

I'm a DSB guy- running a year old tank that's had only 1 water change (back on July 4th). No skimmer, no filter socks, no GFO, no carbon... DSB and macro does it all.


:huh: Trace elements?

I try to do a 15% water change every week, but it comes closer to a 25% water change every two weeks. I get distracted. :]

I use a 100 micron sock on the overflow drain, a Tunze Nano 9002 skimmer, and every few months I run carbon in a Fluval U1 for about 48 hours just prior to a water change. I like to do it prior to the water change to ensure the carbon doesn't lower my magnesium. It'll do that if you use enough of it in a reactor.

No GFO, but then, I've always kept my bioload rather low.

Edited by Whys, 01 March 2012 - 12:04 PM.

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#12
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I'm sold, well as much as I can be in this ever changing world, on the DSB. I'll be setting up my new tank shortly. I get the eggcrate to keep the rock from shifting, but why does it need to be elevated? I'm not good with things like tools and measuring and cutting.


I strongly recommend doing further research before opting for a DSB. There are risks involved and trade-offs to consider. For example, some people like to keep their DSB in their refugium. Not just so they don't have to look at it, but because it can be more easily removed if it goes bad. On the other hand, putting it in a refugium is, IMO, one of the easiest ways for it to go bad in the first place. Those with the space like to put it in a remote bin, but I have strong reservations about placing it anywhere other than in the display. It's my personal belief that any other location vastly reduces its full function. But my reasons are based on reasoning, not peer reviewed science. :)

The shelf is elevated to an inch below the sand bed height. The rocks actually rest on the shelf, not the sand. Base rock is also an option.

Edited by Whys, 01 March 2012 - 11:42 AM.

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#13
Amphiprion1

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I strongly recommend doing further research before opting for a DSB. There are risks involved and trade-offs to consider. For example, some people like to keep their DSB in their refugium. Not just so they don't have to look at it, but because it can be more easily removed if it goes bad. On the other hand, putting it in a refugium is, IMO, one of the easiest ways for it to go bad in the first place. Those with the space like to put it in a remote bin, but I have strong reservations about placing it anywhere other than in the display. It's my personal belief that any other location vastly reduces its full function. But my reasons are based on reasoning, not peer reviewed science. :)

The shelf is elevated to an inch below the sand bed height. The rocks actually rest on the shelf, not the sand. Base rock is also an option.


I agree. Starving a sand bed is probably one of the best ways to make one fail--placing it remotely makes starvation even easier to accomplish. It's good, solid reasoning :)

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kgoldy

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:huh: Trace elements?



I use TLF Iron, Iodine, Stronium+Manganese and Reef Elements... without much consistency. If I feel colors start looking a little drab, I dose all four.

I broadcast feed daily (or twice daily), and I believe this actually contributes to keeping my trace elements at decent levels without water changes. Can I prove this? No. But I must be doing something right. Haha.


What size is your tank? Most people on this forum have too small of a tank to maintain enough diversity for a sandbed to flourish...

Edited by kgoldy, 01 March 2012 - 01:39 PM.


#15
Whys

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I use TLF Iron, Iodine, Stronium+Manganese and Reef Elements... without much consistency. If I feel colors start looking a little drab, I dose all four.

I broadcast feed daily (or twice daily), and I believe this actually contributes to keeping my trace elements at decent levels without water changes. Can I prove this? No. But I must be doing something right. Haha.


What size is your tank? Most people on this forum have too small of a tank to maintain enough diversity for a sandbed to flourish...


That actually sounds like a superior approach. When I have the time, I might want to try that. Water changes have never really been sufficient for maintaining proper Alk anyway, it seems. It's always a little low. But that's partly Oceanic's saltmix. I really should buffer it a little. Also considering Ionic 2 part. Just haven't had the time.

Thanks for the input!

Oh yeah... It's about a 50g system. The display tank is about 36g after sand bed displacement.

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#16
kgoldy

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I forgot to mention- Kalkwasser for the ATO. Duh...

#17
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FWIW, I do believe a DSB can work in a nano tank. The key is ample water flow and a healthy benthic population.

I think the real issue is that DSBs work great, all the way up to a tipping point. They will absorb excess bioload faster than they can convert it, then store it like a battery. Once it's full, the process turns on its head and becomes a growing source of serious trouble.

While I agree that DSBs in a refugium can become starved and non-functional, I actually think the opposite is more often the case. People think DSBs are a great idea, until they come face to face with the volume they take up. So then they get clever, cut corners, and short-change the DSBs requirements. Mostly, they think they can get away with sticking it in a fraction of the space with minimal flow, then use the saved space to add more bioload. It makes for a larger source of nutrients and a smaller sponge for absorbing them. It can appear to work for awhile, until the sponge is full.

I can't prove any of this. :)

Posted Image

Edited by Whys, 01 March 2012 - 02:28 PM.

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What are you using to replenish the bio-diversity in your sandbed?

I've tried GARF (horrible idea), Inland Aquatics, and most recently, Indo-Pacific Seafarms.

Both Inland and IPSF were great, though pricing is pretty insane.

#19
Whys

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What are you using to replenish the bio-diversity in your sandbed?

I've tried GARF (horrible idea), Inland Aquatics, and most recently, Indo-Pacific Seafarms.

Both Inland and IPSF were great, though pricing is pretty insane.


Fiji liverock. It doesn't get much better. :)

Spionid worms reproduce themselves easily, even in the 2.5g display I have on my 7.5g breeder system. Baby stars will also reproduce themselves, and while they don't spend a lot of time on the sand bed surface, they do a play a role in preventing the buildup of detritus. A couple reef-safe hermits are also a must, IMO. They keep stuff from getting buried. Cerith snails are another must. They 'till the soil', as it were, and eat out any algae that can bind the sand and trap detritus.

Ever since I stopped using Flatworm-Exit, I haven't needed to replenish the benthics. There is a kind of burrowing amphipod that makes the shallow tunnels seen here.

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I consider them an indicator species of my sand bed's overall well being. I'm still not certain they reproduce themselves. FWE always wiped them out and only the live rock seemed to replace them. But I haven't used FWE in over a year now, added my last piece of live rock shortly after that, and I still have some of the burrowers, just not as many. So I can't say if they reproduce or are simply long lived.

If I were more focused on my display tank right now, I'd probably buy a 20 lbs bag of OceanDirect to liven things up. It's all micro fauna in the live sand, but they are essential for supporting many of the benthics farther up the food chain. The micro fauna does not reproduce itself effectively and fades away over the course of several months.

Edited by Whys, 01 March 2012 - 03:55 PM.

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#20
Amphiprion1

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What are you using to replenish the bio-diversity in your sandbed?

I've tried GARF (horrible idea), Inland Aquatics, and most recently, Indo-Pacific Seafarms.

Both Inland and IPSF were great, though pricing is pretty insane.


IME, Inland is the better of those for certain in terms of overall diversity, but very expensive as you say. That's how I got my capitellid worm :) I also introduced some sand from and LFS and some "gunk" from their live rock bin. Seemed to do the trick, as the latter is what introduced a lot of cirratulids--I have several individuals per square inch of space, not including amphipods and other worms, such as amphinomids and dorvilleids.

#21
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That's how I got my capitellid worm :)


How deep does that thing dig? Any idea?

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#22
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How deep does that thing dig? Any idea?


I've seen it at about 5" at the deepest, so near the bottom--probably even to the bottom. It is quite big, too.

Edited by Amphiprion1, 01 March 2012 - 05:13 PM.


#23
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I've seen it at about 5" at the deepest, so near the bottom--probably even to the bottom. It is quite big, too.


Nice. Earth worms of the sea. How big is big? Think it could survive on 3 square feet? I wonder if it might deliver too much oxygen to the hypoxic regions.

Ever burrow along the glass?

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#24
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Nice. Earth worms of the sea. How big is big? Think it could survive on 3 square feet? I wonder if it might deliver too much oxygen to the hypoxic regions.

Ever burrow along the glass?


It is (roughly speaking) a bit smaller in diameter than one of those fat pencils you can get kids. I don't know the total length, but I've seen 6" at one time and, yes, it was against the glass. I got to observe its proboscis gulping in some sediment, too, which was pretty cool.

As far as how much it disturbs the stratification, I have no idea. Makes me wish I had an O2 probe to test that. I'd imagine with the seagrass roots on top that can potentially completely choke out the bed, it probably stays low in oxygen no matter what. That is, until I uproot things and disturb it. Luckily, everything is hardy and reestablishes itself comparatively quickly. It's not even something I really do monthly, so it has a reasonable amount of time to recover and it isn't nearly as debilitating as something like vacuuming it.

Edit: forgot, but here's a terrible picture of him--he was moving quickly because of the light, so I snapped it pretty fast

Posted Image

Edited by Amphiprion1, 01 March 2012 - 06:47 PM.


#25
Whys

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That's a great photo! Thanks for sharing it.

Sea grass with earth worms... now you just need the proper croquet set.

Posted Image

What's the footprint of that aquarium?

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