FAQs on Sandbed Dimensions

Discussion in 'Biological/Natural Filtration and Deep Sand Beds' started by sihaya, 26 Mar 2009.

  1. sihaya

    sihaya

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    I'd just like to start this thread/post because it seems like there's a few very common misunderstanding regarding the ideal dimensions of a DSB... and I feel like I'm repeating myself. So let me just clarify for all here...

    1) Deeper is not always better: The depth of the sandbed is only one factor in the functionality of a DSB. The depth should be at least 10cm. But deeper is not always better... you will not gain much (if any) more functionality past 15cm. If you have a DSB much deeper than 20cm, you might get issues with water not getting down to the bottom (and could end up with "cement" at the bottom of your sand bed).

    2) Finer sand is better: Unfortunately, almost all substrates sold in our hobby as "marine sand" are coarser than is ideal for a DSB. The ideal grain size is more like that of mud than what we think of as sand. However, "mud" has its own troubles (it's hard to keep down and can get messy)... and it's not easy to find. Thus, when I look for sand, I look for the finest sand available (and errr... cheap) that I can still keep "under control."

    3) Bigger is better than deeper (after 15cm of depth): If you want to increase the functionality of your DSB, make it bigger... not deeper. Increasing the "footprint" of your DSB will increase the area of the interface between the surface of the sand and the water. I hear a lot of talk about water flow over a DSB... well, you can increase the water flow all you want, it's only going to do so much good over a limited surface area. The smallest sand bed should be at least approx. 92cm by 46cm... or some such dimensions that add up to the same square area. This is the minimum no matter what size tank you are keeping. If you have a nano tank and want a DSB, you'll likely have to set up a remote DSB. For bigger tanks, *ideally* the DSB should have the same (or bigger) foot print as the display.

    4) Flow is important, but not everything: You definitely want to have good waterflow over your DSB, but you don't want so much that you're constantly disturbing the surface of the sandbed (and/or creating sand clouds). There's not a whole lot of "for sure" info on just how much flow a DSB needs. Personally, I would use as much as you can without disturbing the sand itself. And as stated above, increasing the waterflow over your DSB will only do so much good over a limited surface area. To a point, you're not going to do yourself much more good increasing your waterflow from 380lph to 2271lph, if the surface area of your DSB is only 30cm by 30cm.

    Cheers,
    Sara M.
     
    Last edited: 26 Mar 2009
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  3. dallasg

    dallasg Moderator MASA Contributor

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    Thanks Sara, really awesome info, so looks like a minimum of 40-50 cm2 for the dsb. I do agree that surface area is far more beneficial then depth.
    What I have tried is using sea sand and estuarie mud and used plastic insect netting to keep it from flying away in the flow and a lite layer of superfine aragonite to weight it all down. Will see the results of that now that I am cycling a new tank.

    So a good rule of thumb then is to have the same size square meter of sand as your tank base, and if one can have as big as possible.
    Posted via Mobile Device
     
  4. sihaya

    sihaya Thread Starter

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    Thanks dallasg... I've never tryied putting netting over the sandbed... but it sounds like a decent idea (as long as the sand bed can still "breath" through it). It should be able to... I mean, as long as the "holes" are big enough... don't see why not...

    I do really wish there were more "studies" (even anecdotal) about these kinds of things. It might be a good idea for some kind of collaborative effort...

    Regarding "rules of thumb"... I generally hate them, but if I had to come up with one, let me "refine" my earlier "rule" of having a sand bed = to the base of the display tank. Instead, I'd say, try to have 9 to 16 sq cm of sand bed surface per liter of water. So, for example, suppose you have a 150 litre tank... that would work out to be, roughly, 1875 sq cm of sand bed (which works out to be about the same as the dimensions of the base of a 150litre tank). I would use this instead of going by the base of the display alone because some tanks are taller than others...
     
    Last edited: 26 Mar 2009
  5. Tobes

    Tobes Retired Moderator

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    Hi Sara, in one of your previous posts you said a DSB needs to be roughly 2000 square cm. I quoted your post.


    "You're sump might hold 80g, but maybe I'm not being clear... it's not so much the water volume that matters. It's the area of the sand bed. The length and width of the sand bed (the "foot print") should be at least (roughly) 2000 square cm... if that makes sense."

    In this thread the calculation works out to 4232 square cm (92 x 46) and now you say that it needs to be 3 -4 sq cm for every litre of water?
    I'm confused now as there is a big difference between 2000 and 4232 and 3-4sq cm for every litre.
     
  6. dallasg

    dallasg Moderator MASA Contributor

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    thanks Sara, i am a big believer of dsb's, i have a 6ft and 5ft running off a 1.2mx1m 13cm deep dsb which is way bigger than i need but will provide more prestine water params
     
  7. sihaya

    sihaya Thread Starter

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    Editing this post...

    Yikes... we're confusing "cm squared" with "square cm." Ok, so the minimum DSB should me... 40 to 50cm squared... OR 2000 square cm... roughly.
     
  8. Tobes

    Tobes Retired Moderator

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    Yes, but 40cm x 50cm is 2000 square cm :p - and you have two multiply the one with the other to get surface area.
     
  9. sihaya

    sihaya Thread Starter

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    Wait, I know what's going on here... I/we are getting "40 to 50cm squared" mixed up with "square cm." 40 to 50 cm squared is 1600 to 2500 square cm.
     
  10. dallasg

    dallasg Moderator MASA Contributor

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    w.r.t your first post, 92cm x 46cm gives us a surface area of 0.42m2
    would it not be easier to make it 1mx0.5m by 10cm the default size :)
     
  11. sihaya

    sihaya Thread Starter

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    I want to say yes... but my god, I'm getting myself all confused. So let me go back to the American units for just a sec...

    The minimum DBS should be 10cm depth of sand in a 40g breeder tank... which is 36 inches long x 18 inches wide.

    Will someone please translate this into metric before I hurt myself? I thought I did this already... but something got mixed up. Thanks.
     
  12. dallasg

    dallasg Moderator MASA Contributor

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    lol

    90cm x 45cm
     
  13. sihaya

    sihaya Thread Starter

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    Oh come on... I said "92cm by 46cm"... I was pretty damn close! So where did I/we get messed up here?
     
  14. dallasg

    dallasg Moderator MASA Contributor

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    i never got confused, i understood perfectly
    my calcs were right, and so were your figures
     
  15. RiaanP

    RiaanP Moderator

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    I got a 90L Display tank
    and DSB area in sump is 32 by 37 cm. That is 12.6" by 14.6" roughly. Is that big enough?
    Yes I got a scrubber, and a skimmer in the sump area.
     
  16. RiaanP

    RiaanP Moderator

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    giving just under 1200 square cm
     
  17. dallasg

    dallasg Moderator MASA Contributor

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    how do u get that?
    isnt the surface area lxb? we talking surface area of sand that water touches arent we?
     
  18. Tobes

    Tobes Retired Moderator

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    He was correct Dallas, 32cm x 37cm = 1184 square cm... and he said just under 1200 :p
     
  19. dallasg

    dallasg Moderator MASA Contributor

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    i see, sorry busy working in cubic meters at the mo and getting confused with my conversions :)
    i hope the chemicals in my plant dont explode :whistling:
     
  20. sihaya

    sihaya Thread Starter

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    LOL... no wonder Steven Pro demanded to see proof that I have a MA in Mathematics... I swear I do!! Only goes to show you how little practical knowledge a liberal arts education will give you... lol j/k!
     
  21. dallasg

    dallasg Moderator MASA Contributor

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    isnt also true that if your dsb is too deep the bottom parts build up sulphur?
     
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