Deep Sand Beds (DSB)

Discussion in 'Filtration Articles' started by Reef Maniac, 6 Feb 2010.

  1. Reef Maniac

    Reef Maniac

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    Deep Sand Bed (DSB)

    The correct term should actually be a Deep Live Sand Bed (DLSB), because the sand bed can only operate properly if it is populated with appropriate sand-living organisms. But I'm jumping ahead of myself, so lets start at the beginning...

    Aim of a DLSB

    The aim of all filtration systems is to reduce potentially toxic biological waste produced by our tank inhabitants to less harmful, or even better - totally non-toxic, products. In our tanks the waste from our fish and corals, and uneaten food, is quickly converted to ammonia/ammonium (depending on pH), which is highly toxic even in very low concentration. Aerobic (oxygen loving) bacteria in the tank can fortunately convert this ammonium into less toxic nitrite, which other aerobic bacteria then further converts into nitrate. Although nitrate is not very toxic for fish, it does have the potential to cause massive algae blooms, and is still rather toxic to corals and other invertebrates. Unfortunately, this nitrate can only be further broken down by anaerobic bacteria, which only live in areas where the oxygen level is rather low (but not totally absent...).

    Both the aerobic and anaerobic bacteria need two things in order to multiply - enough food (the waste products) and enough suitable substrate "living space" (the rock or sand). In our natural filtration systems, we use live rock and/or live sand to act as substrate for both the aerobic and anaerobic bacteria. Because of it's size, a given volume of fine sand has a much larger surface area than the same volume of rock, and can house much more bacteria than the rock - thus making a sand bed a *much* better filter substrate than live rock.

    Aerobic area

    With good water flow in the tank, the surface of the sand bed (and live rock) continuously receives highly aerated water, and this water can slowly permeate into the sand bed (and into the interior of the live rock). This water is rich in oxygen, and readily supports a dense growth of aerobic bacteria which then uses the oxygen to convert the ammonium to nitrites and then to nitrates. During this process the oxygen is used up, and as the water moves further into the sand bed or rock it becomes more and more anaerobic (oxygen poor). At some depth, depending on the grading of the sand and the flow of water above the sand bed, the oxygen concentration in the water drops to a level where anaerobic bacteria can live and multiply, and where they can then convert the nitrates (which are in solution in the permeating water) into inert nitrogen gas.

    Anaerobic area


    As stated earlier, our anaerobic bacteria live in oxygen poor water - but importantly, they still need *some* oxygen. As a sand bed becomes deeper still, the concentration of oxygen can decrease to a level below where these anaerobic bacteria can live and multiply - this is the so-called anoxic region, and it is inhabited by anoxic bacteria. These bacteria "breathe" sulfur, and in even more anoxic regions they can actually "breathe" calcium (but the latter only occur at really great depths in the oceans, and I have never heard of them living in our tanks...). Despite the old-wives tales and "mythology", these anoxic bacteria are actually very beneficial to our systems, as they not only convert nitrate into nitrogen gas, they also convert toxic heavy metals into non-toxic (and less soluble) metal salts.

    Hydrogen Sulphide

    "OK", you may ask, "but what about the toxic hydrogen sulphide gas and black areas in the sand?" Well, hydrogen sulphide IS pretty toxic if released into the water in a large volume. Fortunately, when a DLSB is operating properly, this gas is used up again by some of the bacteria, and/or is continuously released into the water in very small quantities which is totally non-toxic. It is only when the sand bed is "stirred" by either the aquarist, or by a large "sand sifting" fish or other animal (which should not be kept in a DLSB tank in the first place...) that there is a chance of a toxic gas release.

    Contrary to popular belief, the black areas in the sand are also NOT indications of hydrogen sulphide production. The H2S gas is colourless, and can not turn the sand black. The black/brown/darkly coloured areas are actually caused by the anoxic bacteria converting metals, such as manganese (black), iron (red/brown), etc. into harmless manganese oxide, iron oxide, etc.

    Life in the DLSB

    "Right, now what about the "Live" in the DLSB?" The deep sand bed needs a constant, but very light, water flow through it, from the surface right down to the deepest part of the bed. This is achieved by the "pumping" and "crawling" action of the sand-living organisms in the DLSB. A mature, well-operating DLSB has literally thousands (if not tens-of-thousands...) of sand-living creatures, ranging from large polychaete (bristle) worms all the way down to microscopic flat worms, amoebas (if there are salt-water amoebae??), etc. in every cubic centimeter of sand. All these "critters" continuously move around in the sand, and the larger worms also "pump" water through their bodies whilst feeding (or breathing), and although each individual movement is quite insignificant, the total movement of all the critters can displace (and circulate) a surprisingly large volume of water.

    A second reason for needing sand-living organisms in our DLSB is that they EAT. The larger worms would eat fish excrement, left-over food, and other "waste". Their waste is then eaten by the smaller copepods, whose waste is in turn consumed by micro flat worms, then by the single-celled organisms such as the amoeba... and so it goes all the way down the food chain, until the "waste" has been converted into nice "bite-size" portions for the bacteria.

    In summary


    To summarize - a successful DLSB needs the following: Properly graded, fine sand with all the particles having smooth, rounded surfaces - in other words, a "natural" sand such as real sea sand, river sand, etc. and NOT crushed sand (which have sharp edges due to the crushing process...). A total depth of between 75mm and 300mm, with the most recommended depth being between about 100mm - 150mm. A proper "seeding" with either live rock, or preferably live sand imported from a reef with many of it's critters. It is also a good idea to swap small amounts of sand with other aquarists, as this can increase the bio-diversity in the sand. Good water movement over the surface of the sand bed. No sand sifting fish or other creatures, and NO siphoning or stirring of the sand bed by the aquarist.

    This has only just "skimmed" the surface of having a successful DLSB, but I hope that it has been of some use in clarifying this very interesting subject.


    Hennie
     
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  3. Tobes

    Tobes Retired Moderator

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    Thanks Hennie, easy to read and to understand. Will help the noobs a lot. Well done Uncle!
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  4. lanzo

    lanzo Sponsor

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    Very nice....Thanks hennie:thumbup:
     
  5. Broder

    Broder Mudshark

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    Thanks for the beautifully written, easy to understand introduction to DLSB. There are a couple of things that I'd love to hear your thoughts on:

    1. Do sand beds have a life-span of usefullness, ie. should they be replaced after a set time? Or should we just monitor the visible organisms, and take action if their numbers dwindle?

    2. How does the efficiency of a DLSB compare to an algal filter where nitrate is converted with the process of photosynthesis into oxygen? This question is not aimed at promoting one over the other as they're both, IMO integral in a reef system, but rather comparing rates of absorption.

    3. What is your opinion of esturine mud beds as part of a deep live sand bed. Are the particles too dense to allow any real bacterial action between it and the water, considering that there isn't much "stirring" going on by critters?
     
  6. OP
    Reef Maniac

    Reef Maniac

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    thanks guys - this is actually an old article which has been on MASApedia since it's inception - Viper asked that we move our articles into this forum - that's all that I've done at this stage :whistling:

    As with just about everything else in this hobby: "It depends..."

    My DLSB (well, a large portion of it...) is now more than 10 years old. I have added some more sea sand over time, just to increase the depth a bit, but the bulk of the sand is still the same old stuff I collected off the beach at Jongensfontein (near Stilbaai) when I started this hobby. When I moved to Bloemfontein from the Cape south coast some 6+ years ago I transported the DLSB in some buckets, and just carried on using the same sand, with some river sand added when I changed to a larger tank at the beginning of 2005. Each time I moved the sand I did lightly rinse it in old tank water, but it still looked pretty dirty after the rinse. Five years since last disturbing the DLSB, my tank's ammonia, nitrite and nitrate levels are still below the detection limit of our hobby-type test kits...

    To answer your question, I believe that a DLSB can remain viable indefinitely, IF you have a large enough bio-diversity in the sand bed, and (of course) if the sand bed is not over-loaded past it's filtration capacity. This implies that one should:

    • not keep "DLSB predators" such as most wrasses, mandarins, "sand sifting" starfish, gobies, etc. if the DLSB is in the display tank. If it is a remote DLSB, then of course this does not apply.
    • replenish the sand-living fauna from time to time, either by adding small quantities of sand from fellow reefer's tanks or by adding small bits of fresh live rock rubble. Ideally, one should try to get some of the "grunge" left over on the bottom of the boxes that LR is shipped in to the dealers.
    • not over stock one's tank, especially with fish.
    • maintain a refugium of some kind (in-sump or dedicated) to help replenish the life in the sand bed.
    I'm biased towards the DLSB, so don't take my word as gospel ;) but I believe that a mature, well set up DLSB is more efficient than an algae scrubber of the same volume. It is also cheaper, as you do not need any additional lights or pumps to make it work. As stated in the article, a DLSB can also remove/bind toxic heavy metals (better than an algae scrubber, I believe...) On the other hand, an algae scrubber does remove more phosphates than a DLSB, so the ideal would be to have both, or at least to also have a good growth of algae in a refugium.

    A properly graded DLSB must contain a (small) percentage of mud, but I would not use a mud bed as part of a DLSB. Used separately (in it's own chamber in the sump, or wherever), it can be beneficial, but then one must have the correct mud-living animals to live in it. Research by amongst others Dr. Rob Toonen (if memory serves) has shown that the largest bio-diversity of infauna is achieved in a rather specific sand gradation, and that there are relatively few animals that live in the mud. The mud bed can be much shallower than a conventional DLSB, though, so in some cases it might be the best option to use. I have never tried a mud bed myself (yet...), but envisage that a mud bed on the bottom of a "settlement chamber" could be quite useful, especially if it contains one or two mud- or sand prawns that can filter-feed on the settling detritus.

    Hennie
     
    Last edited: 6 Feb 2010
  7. lanzo

    lanzo Sponsor

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    i have a mud bed just before my DSLB.... The amount of pods/bristlewroms in my MB is much more than on my DSLB.

    Can this be due to all the solids settling on the MB first or does it have something to do with the minerals or the tecture of the mud that they like more?
     
  8. Broder

    Broder Mudshark

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    My finding is the opposite of Lanzo's. The mud bed in the DLSB started off with a lot of life in it, including prawns and worms, but gradually these died off, and it now appears dead on the surface. I'd love to have access to a microscope to "scope" the bio-diversity, if any, that is left.
     
  9. Warr7207

    Warr7207

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    cool thread
     
  10. OP
    Reef Maniac

    Reef Maniac

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    I would guess it's the free food - always good for attracting a crowd :whistling:

    Seriously, though - you are describing animals that live above the sand/mud bed. The real infauna which lives IN the sand- or mud bed would be creatures such as worms, microscopic multi-celled and single-celled organisms, and bacteria - also various forms of algae within the top 10mm - 20mm of the bed. Because of the small size of the mud particles, it will pack very dense, and restrict both the movement of larger small critters such as the various worms, and the penetration of water (thus restricting the availability of food and oxygen).

    I have not done so for a while, but I regularly check the microscopic life in my DLSB. On average, I find between 5 and 20 microscopic critters in every drop of water taken from about 10mm below the surface of the bed (and that excludes the "giants", such as small bristle worms, which just does not fit in a drop of water...). I can really recommend a microscope for anyone interested in the complete marine system - it certainly opens up a new world of life-forms which would otherwise have remained unknown.

    Here are some examples:

    A single grain of sea sand - note the smooth, rounded surface, the cracks/fissures in the grain, and the growths of micro-algae:

    1094b6d680e10748.jpg


    A foraminiferan (the curled tube in the middle of the photo), a micro-starfish and a ciliate-type gogga to the right. There are at least two other critters visible (although out of focus):

    1094b6d6840aeb95.jpg


    A micro-flatworm busy eating detritus, and another micro-starfish:

    1094b6d6879b4b0c.jpg


    An unknown "gogga":

    1094b6d68c183d67.jpg


    A bristleworm larvae:

    1094b6d6906d3fc8.jpg


    Hennie
     
  11. Mauritius-aquarist

    Mauritius-aquarist

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    Hey reef maniac, really nice to share the pictures, frankly fantastic:thumbup:
     
  12. Neil H

    Neil H Moderator

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    Wonderful article Hennie,

    Perhaps a Doff question ..... the fish produce the waste, the bacteria convert the waste to something not hamfull to our systems... what is this "something"? with a LNS (yes i know i keep going on about this) the bacteria produce mulm as the less harmfull waste which ... what is the DLN version of mulm?? or do i have the cat by the tail???
     
  13. Warr7207

    Warr7207

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    WTF. Is this some sort of Mixt talk ?
     
  14. Neil H

    Neil H Moderator

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    :lol: I honestly wish it was ..........

    a correction to my statement is that DLN should be DLSB.... bloody :peroni: got the better of my typing fingers
     
  15. OP
    Reef Maniac

    Reef Maniac

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    No, quite the contrary :whistling:

    Definition in About.com:

    Definition from The free freshwater and saltwater encyclopedia:

    From Albert Thiel's book "Small Reef Aquarium Basics", written some 20+ years ago:


    So, depending on how you define it, mulm is either the un-decomposed fish waste (although I would rather define that as detritus), or the totally mineralized (cannot further decompose) remains of the processed detritus (which is the definition I prefer to use).

    After working for some years, the deep sand bed certainly looks VERY dirty when disturbed, and one could be forgiven for thinking that this "waste" is totally bad, and the cause of all evils in the tank. IMHO, the contrary is actually true - let me explain...

    A large percentage of the fish waste (and other primary waste, such as coral slime...) is removed by the protein skimmer. The rest of this detritus settles onto the DLSB, where it is processed by the sand-living organisms. Each organism can extract between 10% and 20% of the nutrients that it eats. So, lets say that (as an example) a large bristle worm eats a piece of fish poo. The worm's excrement would thus contain (say) 90% of the nutrients that the fish poo had. Now a copepod eats the worm's poo, and deposits it's waste which now only contain (say) 80% of the original nutrients. If this food chain is long enough (and in a healthy, well set-up DLSB it can easily be...), it would only take five to ten critters to change the detritus into mulm. This mulm looks bad if the sand is disturbed, but it has now become pretty inert.

    Judging from personal experience, the mulm does not accumulate indefinitely, because there is no visible build-up on my sand bed after all these years of being in operation (or perhaps it is still building up, and will only become visible after (say) 15 or 20 years, who knows...).

    Here's another (contradictory) thought - perhaps the mulm does break down into it's chemical components - but this would not be a bad thing either... Why pay a lot of money to dose various mineral additives (trace elements...) if the mulm is supplying these in minute, but constant, doses? Perhaps this is the reason why my tank has been doing so well for so long, without ANY additives apart from alkalinity, magnesium and calcium...

    Hennie
     
    Last edited: 7 Feb 2010
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  16. RiaanP

    RiaanP Moderator

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    What happens to the end result of detritus?

    Copied from an article on Cryptic zones from Latest | Practical Fishkeeping

    So this is mostly the dirty stuff you see when you disturb a DSB.
     
  17. Warr7207

    Warr7207

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    Thanks
    hamfull and LNS ?
     
  18. OP
    Reef Maniac

    Reef Maniac

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    You're being difficult now :whistling:

    First one is obviously a spelling mistake (come on, you knew that...)

    LNS = Low Nutrient System - in other words, those bright, multi-coloured frag menageries that everyone is trying to create (sorry Neil :biggrin:) MASA has a whole section dedicated to this: Low Nutrient Systems - LNS / ULNS - Marine Aquariums of South Africa

    Hennie
     
  19. Warr7207

    Warr7207

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    Sorry I didn't know these. In the context of the post, I couldn't see that it was a spelling mistake.

    Probably don't know LNS, cause I have never tried to run a Low nutrient system, I believe in having lots of FAT fish :p
     
    Last edited: 7 Feb 2010
  20. OP
    Reef Maniac

    Reef Maniac

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    Ja, you know how these geologists are - spend 99.72% of their time talking to rocks, so we can't expect then to be able to spell, you know :biggrin: :biggrin: :biggrin:

    Ducking now, cause Neil is much bigger than me...

    Hennie
     
  21. Neil H

    Neil H Moderator

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    ok ok, so a geologists spelling is shit .....

    thanks Hennie et al for the explanations ....

    From what i am reading mulm is referd to as something slightly differently in the LNS .... but again, everything you read is slightly different, which one do you believe ???

    " in other words, those bright, multi-coloured frag menageries that everyone is trying to create (sorry Neil :biggrin:) "... ag neee man Hennie, they are not all like that i really believe it is the way of the future ....:):)

    Warr, LNS does not mean low feeding, ironically LNS is perhaps one of the poorest descriptions i have every come across, in reality LNS should be renamed to something like a NNS (natural nutrient system) or RNCS (rapid nutrient cycling system)..... any healthy marine system has plenty nutrients, a LNS system simply cycles these nutrients extrememly efficiently, this can be achieved with the zeo system (which scares the shit of of everyone because of all the technical terms and dosing regieme.....) OR with an extremely well maintained and well functioning DSB.......

    Sorry mods if i have taken this thread off topic, feel free to move some of this across to the evil LNS section:razz::razz::razz:
     

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