Deep sand bed

Discussion in 'General Discussions and Advice' started by koi500, 28 Jan 2008.

  1. koi500

    koi500

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    Hi hennie, can you give me a brief explanation on the concept of running a deep layer of substrate to improve filtration? my experiece hasbeen if the substrate is thick and dead water spots develop you get black and smelly sand under the top level of sand ? is this "un aerobic" and therefore dangerous to fish eventually? excuse the ignorance but im really interested in using it if its good for the tank as i have plenty of room in my filter box _ as well as water movewment _ appreciate your comments cheers dave nyland
     
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  3. Reef Maniac

    Reef Maniac MASA Contributor

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    Hi Dave, I've moved this message into a new thread - hope you don't mind.

    I will gladly give you an explanation of the workings of a deep sand bed, but I'm afraid it might not be very brief



    OK, lets see...

    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.

    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.

    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.

    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.

    "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.

    "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, amoebae (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.

    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... so fire away with further questions, if necessary...

    Hennie
     
  4. koi500

    koi500 Thread Starter

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    hi hennie thanks, hope im asking questions in the correct forum? have measured the interior of the sump and have enough free space to accommodate a plastic tray 95cm in length by 50 cm in width and can go up to 18cm in depth of tray - then my return flow of water will move accross the surface of the tray and hopefully carry all the waste from the tank to the surface of the DLSB - i think i have some of the reasoning behind this type of filter bed but (1.) what should i use as depth of sand and (2) how do i seed my sand? and (3) how do i know its working correctly?
     
  5. jacquesb

    jacquesb Retired Moderator

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    Hi Hennie - I know that this is your forum - I just want to say "thank you" for the decent and in-depth explanation. I enjoyed the read.

    In response to Dave's question - I am sure that you would agree - the answer is "YES" - that IF Dave can fit this plastic tray into his sump, he can fill this tray up to (I would say 150mm) at least a few mm from the top with the "correct" sand material.

    Hennie - thanks again - I think that the importance of a DSB is extremely understated in this hobby!
     
  6. Reef Maniac

    Reef Maniac MASA Contributor

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    No, this is OUR forum - all of us - and I appreciate any input from other MASAdonians... so please feel free to answer questions, add info, comment on answers given, and generally participate on this forum :thumbup:

    Hennie
     
  7. Shaun

    Shaun Retired Moderator

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    Hi Hennie hope you don't mind (if you do tuff:whistling:) Just been reading AC's book and he mentions the size. Min 20% of main tank reccomended 40% or bigger, and no light on DSB.

    Any comments?
     
  8. Reef Maniac

    Reef Maniac MASA Contributor

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    Always glad to help, and yes, any marine related question is welcome :)

    A tray of that size would work fine, but you don't really need to use a tray (unless you want to...), just placing the sand directly into the sump will work just as well.

    1.) The depth of the sand DLSB would depend to a great extent on the grading (particle size) of the sand. If you're using a fine sand then a depth of 150mm would be more than adequate.

    2.) Much of the life in the sand will migrate there from the live rock, but the best way would be to buy a small quantity of live sand from one or two reputable dealers. You could also beg/steal a bit of sand from as many other hobbyists with DLSB's as you can - this will increase the bio-diversity of the sand bed.

    It's also a very good practice to "refresh" your DLSB at least once every year by adding small amounts of newly bought live sand - this would replace some of the species which became extinct in your tank for whatever reason.

    3.) Your ammonia, nitrite AND nitrate levels should be close to zero - undetectable with normal hobby-grade test kits (nitrate less than 10ppm, and more likely at 0 ppm). You should also see small bubbles forming between the glass and the sand - this is the nitrogen gas produced by the conversion of nitrates). After some time you should also observe dark areas in the sand - this is a sure indication that the sand at that depth has become anoxic, and that the nitrate reducing bacteria are hard at work.

    Hennie
     
  9. Reef Maniac

    Reef Maniac MASA Contributor

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    No, you mean tuff shit - watch out, I will :76: ... but seriously, as stated above, I really don't mind :)

    Well, you know the Yanks, they always like to do things bigger than anyone else (sorry Sara ;) ). I don't think that one should really be blinded by specific figures - after all, the surface area of the sand is what's important, and a smaller area with a very fine sand would most likely outperform a larger area with courser sand particles. Having said that, I do agree with Anthony that, all else being equal, more is better. To me the ideal would be to have a shallower DLSB (say 100mm - 150mm) over the total area of the display tank (water current permitting...) AND a deeper DLSB of 200mm - 250mm in the sump.

    I do NOT agree with the "no lights on DSB" statement, and I would be rather surprised if that is his recommendation. You do not need very strong lighting, but knowing that micro algae live to quite a depth inside the sand bed, and this algae being both food and a consumer of nitrate and phosphate, I would definately recommend having good lighting over the DLSB. In fact, the ideal would be to have a DLSB, and to have macro algae growing above it, IMHO.

    Hennie
     
  10. nakoma

    nakoma

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    i wll visit here alot thanks for the great info :thumbup:
     
  11. Shaun

    Shaun Retired Moderator

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    I thought I was going nuts as I could not find the info again:blushing:
    but here it is.

    Pg 60 Reef Invertebrates

    "The simplest refugium for NNR are filled with deep sugar-fine sand and kept unlit. Here,the primary purpose is nitrate reduction. The absence of (dedicated) light reduces the ability for autotropic nuisance algae to gain a foofhold. It also spares the need for much or any support from detritivores (sand-stirring creatures......."


    I thought I was going nuts as I could not find the info again:blushing:
     
  12. Reef Maniac

    Reef Maniac MASA Contributor

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    You're right, we don't want anything to gain a FOOFHOLD in our tanks :lol: :lol: :lol:

    More seriously, though, what is wrong with having "nuisance algae" growing in a sump/refugium? In a tank with good water quality, the most likely "nuisance algae" to grow in and on the sand are diatoms. Diatoms are very efficient users of nitrate and phosphate, and can quite often out-compete green hair algae, and even cyano-bacteria for these nutrients. Diatoms, being microscopic in size, can be easily removed from the water by skimming, thus allowing for the active export of nutrients from our tanks. A second great thing about diatoms, is that they form one of the basic "building-block" foods in the food chain, being eaten by many zooplankton and other small critters. These small critters then multiply, and/or are eaten by larger organisms, including many corals, thus the diatoms are directly and indirectly benefiting the system... so, why would anyone want to prevent an efficient nutrient filter and live food source from flourishing in a sump or refugium??? I am always amused by people who really go out of their way to remove or prevent diatoms from growing in their tank, and yet pay through their noses to buy phytoplankton to feed that same tank :whistling:

    If the "nuisance algae" turns out to be green hair algae, it is still a good nutrient export mechanism, as it is very easy to remove hand-fulls of green hair algae from the sump. Green hair algae also make a very good feeding/breeding ground for small critters. As far as the nutrient levels in the water are concerned, there really is no difference between removing it via caulerpa, chaetomorpha or green hairy algae.

    Like many other things we do to our tanks, there are usually many ways to achieve the same end result. So, keeping a sump DLSB well lit, or in the dark, either way can probably work, it's a simple matter of choice for YOUR particular situation and reefkeeping philosophy :1:

    Hennie
     
  13. koi500

    koi500 Thread Starter

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    Hi Hennie, again just a point before i start building my DLSB filter, where its situated there is only be daylight and only shade during the daylight hours. have no plans to use lighting over this sump unless its absolutely critical for the success of the DLSB!
    im not really keen on artificial lighting and given the total depth of my sump box 1.1m
    its gonna be a real problem to get sufficient light onto the sand surface if thats whats needed?
     
  14. Reef Maniac

    Reef Maniac MASA Contributor

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    Well, you don't really NEED to have light for a successful DLSB, but I do belief that lighting the sump/DLSB would be beneficial, ESPECIALLY if you also introduce some form of macro algae. You don't need fancy lighting, though - a couple of "normal" energy saver lamps will be sufficient.

    If you don't want to use any lights, I would still suggest that you try and obtain some form of day/night lighting change, even if it's only indirect light coming through a window. I don't have any conclusive proof, but I do believe that many of the sand-living critters only spawn during the night (as do many fish...). So, if there is no day/night cycle you could be preventing a lot of critter growth in the DLSB.

    Hennie
     
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  15. jacquesb

    jacquesb Retired Moderator

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    Hi Hennie - NOW THAT'S SOMETHING THAT NEGATES THE INFORMATION ABOUT HAVING A REVERSE LIGHTING CYCLE FOR THE SUMP LIGHTING....... So, you want to tell me it would be MUCH MUCH better for the critters in my sump to have the lighting off at night-time?

    It makes sense, you know..... So, thanks for enlightening me... I never thought about this...
     
  16. palmerc

    palmerc

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    If you are cultivating macroalgae with the intent of stabilising pH swings at night then it is necessary to light the refugim on a reverse lighting cycle. I can't think of any other reasosn why one would need to do this though.
     
  17. jacquesb

    jacquesb Retired Moderator

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  18. Reef Maniac

    Reef Maniac MASA Contributor

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    No, a reverse daylight cycle would be perfectly OK, as long as the sump is dark during the day - as far as the critters are concerned, they would still have a day/night cycle, just opposite to what your tank has.

    Oh, and something else to consider, while we are on this subject - most of our fish, corals, etc. are sourced from Indonesia, and other "eastern" countries, which have quite a few hours difference from out local time - so the critters in the sump could actually be closer to their natural day/night cycle if the sump is on a reverse daylight cycle than the inhabitants of the actual display tank... Has anyone else ever observed their newly imported fish being active during certain parts of the night, or lethargic during the day, or corals opening during the night and closing in the day for the first week or two after being imported - I believe that they could be suffering from jet lag, just the same as we do when crossing a few time zones...

    Hennie
     
  19. jacquesb

    jacquesb Retired Moderator

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    Interesting! Cool! That sounds quite logical. The problem is, Hennie - that a LOT of the corals we get from LFS' have been in THEIR tanks for a while as well. So, the time we get them, they most likely acclimitized already.....
     
  20. koi500

    koi500 Thread Starter

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    hi hennie, first of all please let me say thanks very, very much for all your help, ive learnt a lot since chatting /reading all the forums but specifically on the DLSB filters vs fluidised beds - ok back to my situation - dont know if im going to move away from a fish only tank just yet, but love the look of the reef systems! have now got two trays 60l x 40 w x 22 deep and i can fit both on the bottom of my sump under the return flow so ALL the return water will flow down and over these two trays (the filter sand surface is 35cm below the entry of the return flow) like to keep the forum informed of progress is this the right place to do so?
     
  21. Reef Maniac

    Reef Maniac MASA Contributor

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    The pleasure is mine :)

    Well, it IS your thread, so feel free to use it as you like.

    I would suggest, though, that we keep this thread for DLSB discussions, as it's always better to keep to a single topic per thread (it makes it much easier for other people to later search for a topic and then get the relevant information without too much "clutter") - so rather post "general" updated in a new thread, either in General Discussions - Marine Aquariums of South Africa or in Members Systems and Setups - Marine Aquariums of South Africa

    Hennie
     
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