How deep must sand bed be?

Discussion in 'Beginner Discussions' started by HendrikKotze, 31 Mar 2008.

  1. HendrikKotze

    HendrikKotze

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    I have started filling up my 500 liter tank this weekend with RO water and it is about 3/4 now. I want to scape the sand bed, but have some questions.
    I have filled it up with 40 kg (1 to 3 mm) and 20 kg (6 mm) crushed coral. It is apparently not the best, by my LFS did not have aragonite.
    Currently the fine coral is at the bottom and the coarse coral are on top and it is about 50 mm deep.
    How deep should it be and should I mix it?
    I would like to finish it before the tank is full.

    Thanks,
    Hendrik
     
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  3. Alfie

    Alfie

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    IMO you can make it as thick as you want to. Did you put the sand in after the water?

    I ask because it helps to get all the air out so that their are no air pockets.
     
  4. Quinton

    Quinton Smarty-pants Newbie

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    You should toss the crushed coral - it traps detritus badly. Get something much finer (ideally aragonite, but you know that already ;-). Shallow sand bed should be approx 15mm deep (or 100mm+ for a deep sand bed, but you probably don't want that). Anything in between can be problematic. Can give you further details if you like, but not right now ;-)
     
  5. sihaya

    sihaya

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    I wish I still had the link to the great in-depth article Dr. Toonen wrote on all this... but basically, the sand bed needs to be at least 3 to 4 inches. At the same time, much deeper than 6 to 7in and you don't get much added benefit.
     
  6. LikesFish

    LikesFish

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    I'd swap the crushed coral and finer sand around - have the finer sand on top. This way you will reach your anaerobic zone sooner...

    But yes it is better to have all fine sand. You mention 1 - 3mm, and 6mm. An ideal DSB should have about 75% particles of 0.125mm in size - way smaller than yours.

    And the sand should be oolitic - i.e. rounded, so that it does not hurt your microfauna.
     
  7. sihaya

    sihaya

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    Ditto. This is also discussed in depth in Toonen's article. Finer sand results in higher bacteria counts. Though it does make it more difficult to prevent sand clouds, dunes, etc. One way to deal with all that is to just use a remote refugium (which is always an excellent addition to any system anyway).
     
  8. Quinton

    Quinton Smarty-pants Newbie

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    Here's the Toonen article you're (probably) looking for:

    Advanced Aquarist's Online Magazine - Feature Article: An Experimental Comparison of Sandbed and Plenum-Based Systems. Part 1: Controlled lab dosing experiments

    But I think we're getting confused here (at least I am). The original posting was asking about a (shallow) sand bed in the display tank (as opposed to a deep sand bed in a sump/refugium). Correct me if I'm wrong. Shallow sand beds are almost exclusively aerobic in their action. Deep sand beds incorporate significant anaerobic bacterial action. There's a lot of literature out there on the production of toxic hydrogen sulphide (H2S) by anaerobic bacteria in deep sand beds. I don't have the article handy now, but I read a very convincing study recently showing that aerobic sand beds should not be much deeper than 15mm to minimize anaerobic action. Deep sand beds should be at least 100-150 mm deep to achieve the full denitrifying effect of anaerobic bactierlal action, and mitigate the risks of toxic hydrogen sulphide expulsion from the sand bed.
     
  9. Warr7207

    Warr7207

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    Interesting Article

    The one statement that stood out for me:

    "We urge hobbyists to develop a good 'BS' detector that will allow you to question information presented to you without any experimental evidence to support it."
     
  10. Alfie

    Alfie

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    Hendrik, is this not your sandbed for the display tank you are refereing to and not DSB as such?
     
  11. HendrikKotze

    HendrikKotze Thread Starter

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    This is for the sand bed in my display tank. Currently about 50 mm deep. I do not have space in the sump for the DSB. I have filled the sump with rock and cermaic rings, which I have also read is not 100% correct?
     
  12. HendrikKotze

    HendrikKotze Thread Starter

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    Thanks. I will read the article tonight.
    What is I removed the coarse coral and added aragonite?
     
  13. Matt

    Matt MASA Contributor

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    toss the ceramic rings, put the rock in your display and made a DSB in your sump.
     
  14. mandarinman

    mandarinman

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    matt that is an alright opinion, i have got my dsb in my tank, cos it works for me, fine media, cos i have experienced larger grain causing higher phosphates, in my naon which i am closing down soon. i prefer having an ecosystem instead of a display tank mentality( both are fine) just think a dsb the size of your tank , lekker, works for me and just think a couple of neon faced gobies munching through the sand the whole day(will make sure the liverock os secure). it would be an option to have a dsb in your sump but if you do not(emphasized)have space it is fine to have one in your tank. ps dont talk about dead spots( if you are tempted) cause in a dsb there is a huge one across the bottom of the whole thing(imo).
     
  15. HendrikKotze

    HendrikKotze Thread Starter

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    I have a sump, but it is not configured for a DSB - it has 2 small chambers between the protein skimmer and the pump chamber. How fine is the media in you tank?
    I am thinking of removing the coarse coral and replacing it with aragonite before I add the live rock?
     
  16. Quinton

    Quinton Smarty-pants Newbie

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    Yeah - replace the coarse coral with fine aragonite, irrespective of whether you decide to go deep or shallow. The data on coarse vs fine is pretty clear - go fine!

    Q
     
  17. mandarinman

    mandarinman

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    good reading quinton, i agree, imo the fine sand prevents detritis collecting and decomposing between large sand particles
     
  18. sunburst

    sunburst

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    Agree. Fine on top..... While the bed is still young its still cool to swop. But do not leave it to long
     
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