What is your head height.

Discussion in 'Biological/Natural Filtration and Deep Sand Beds' started by RiaanP, 31 May 2011.

  1. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    Depth of water between last divider top, and actual water level.
    Let us discuss this as a single topic. Discussion is buried inside this thread,
    Sentari's New Tank - Page 34 - Marine Aquariums of South Africa
    but this is something that always bothered me.

    [​IMG]


    What is yours?

    Reason
    We do not want the water to flow too strong over the DSB. Will blow the sand away and will not allow the things we want to settle out of the water, time to do so. So its not penetrating the sand area.
    And we do not want it too slow either, resulting in too much settlement on top of the sand, in regards of detritus. The nitrates and phosphates in the water will penetrate the sand, but eventually the detritus settlement will "suffocate" it. Block the top layer up. That is why we need to disturb the top layer a little bit, either ourself, or using Nassarius or Whelk snails.

    The rule that was advocated 2 to 3 years ago here on MASA was between 3 to 5 times your display tank volume must go via your sump an hour.

    OK, take 2 tanks, both 500L. Both sumps also keep same water volume. Take this turnover rule, so that gives us a return pump of between 1500 and 2500 L/h. I ignore head height for now. Just take it that both tanks got same head height.
    Now the important part. Tank A sump is 300mm wide by by 600mm long. Tank B is 600mm wide and 300 long. (wide, as in divider length). Both DSB got the exact same footprint. What is the flow rate? Tank A water will flow at double the speed across the DSB compared to tank B. Tank A head height, the distance between glass divider top edge and the actual water surface, will be double that of tank B.

    What is the result. Tank B DSB will have settlement on the sand. Needs to be siphoned out. I believe tank A will have a better DSB, even if the footprint of both DSB are the same.

    So its more about the flow rate. And not the water turnover rate as compared to the display. For Tank B, to prevent settlement, you need to have the same head height of water over the divider as tank A.

    Been here, done that, learned my lesson. For my big tank of 750L, the turnover rule meant that I have to use a pump of between 2250 and 3750 L/h. Divider is 600 wide. I used a 3000L/h pump. And I had settlement I needed to remove manually. It just did not work. Until I added another 3000L/h pump and viola. Settlement crap sorted.

    Do I have a valid argument? That the old turnover rule be re-looked at. And rather a rule for a head height of between 5 to 10mm be more valid? The actual distance, I'm not sure yet, but based on my tank, and the tanks at Dorry Pets, it will be somewhere in that range.
     
  2. AdS Guest




    to hide all adverts.
  3. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    @sihaya, what is your view on this?
     
    Last edited by a moderator: 26 Nov 2015
  4. Sentari

    Sentari

    Joined:
    15 May 2009
    Posts:
    2,084
    Likes Received:
    6
    Location:
    Weltevreden Park, Johannesburg
    Would be interesting for people to measure and give their input about their DSB's. If they feel they work or if they dont.

    If its only settlement we worried about this can be combated. But at the end of the day we would like the water to at least settle so that some water is drawn into the DSB.

    I'm just worried that having too much flow will impead the DSB from actually having time to filter the water and allow the reaction to take place.
     
    Last edited: 31 May 2011
  5. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    Yip agree, too much flow is not good either. So is not enough flow either.

    So where is the sweet point?
    Or how can we measure the optimal range for proper flow.
     
    Last edited: 31 May 2011
  6. butcherman

    butcherman Moderator MASA Contributor

    Joined:
    7 Sep 2009
    Posts:
    11,626
    Likes Received:
    280
    Location:
    Kempton Park
    How about if we amendment this rule as a formula of what the optimal flow rate is per cm width of dsb?
     
  7. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    yip, that will be the end result.
    If we conclude that for example 8mm is the optimal point, then there should be some mathematical calculation that take your width into account and that should give the flow rate needed.
     
  8. leslie hempel

    leslie hempel Moderator MASA Contributor

    Joined:
    7 May 2007
    Posts:
    14,541
    Likes Received:
    285
    Location:
    Gonubie East London
    you will need to factor in the rate that the DSB takes in the water and expells it, how would this be established? this will help you finding the happy medium between rate of flow over DSB vs settlement.
     
  9. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    Its the same thing? Water in and over and out, its the same. Unless I'm mis-understanding you Leslie.
     
  10. leslie hempel

    leslie hempel Moderator MASA Contributor

    Joined:
    7 May 2007
    Posts:
    14,541
    Likes Received:
    285
    Location:
    Gonubie East London

    Im reffering to the rate that the water can circulate and effieciently denitrify the water through the sand eg: pull into and exhale the water from the sand bed..
     
  11. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    ok, got that.

    Where are all the other anti DSB guys? I need your input as well.

    Please indicate if your DSB is/ is not working for you. And the head height you got.

    I'm planning to redo my big tank, and I need to get this part right this time.
     
  12. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    I think I got it. Can use this calculation to calculate the flow rate for both overflow box and the sump dividers.

    flow rate, but in Gallon per minute, calculation is
    Q = 1495 * (H^(3/2)) * (B-0.2H)
    B is the length of the sump or overflow
    H is the height of water above the overflow box or sump divider glass.

    But in FEET.
    So a sump of 400mm wide (1.31 feet) and water above glass is 6mm (0.02 feet)
    this gives me a flow rate of 5.392743 GPM
    using a ratio of 227.1247 to convert GPM to L/h
    and the answer is 1224.825L/h

    water over glass increase in millimetres, increases the water L/h exponentially

    • 7mm, extra 317.85L/h
    • 8mm, add 341.16 onto of 7mm
    • 9mm, add 362.90 onto of 8mm

    Interesting part is that you can use this to calculate what your return pump actually deliver back to the display.

    Another interesting part is that doing this calculation on your overflow box and on the last divider in your sump, should both give the same answer. Unless you got reactor pumps or ATS feeder pumps in last chamber that falls back into other parts of the sump.

    Now, to get this Q= .... for metric calculations.

    And I need to go and test this tonight.
     
    Last edited: 1 Jun 2011
  13. butcherman

    butcherman Moderator MASA Contributor

    Joined:
    7 Sep 2009
    Posts:
    11,626
    Likes Received:
    280
    Location:
    Kempton Park
    Riaan That formula only proves one thing....you never work :tt2:
     
  14. RiaanP

    RiaanP Thread Starter Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,158
    Likes Received:
    1,230
    Location:
    Centurion
    well, hmmm, yes...

    spend a lot of time today searching for that.... Do not tell my boss.:blush:
     
Recent Posts

Loading...
Similar Threads - head height Forum Date
Head Heights and Lows with ATO Pumps and Waterflow 4 Dec 2012
Skimmers - Pump head height Theory? Anything DIY Related 6 Apr 2010
[wtd] Hammer head donation Wanted 12 Nov 2016
[wtd] 1500/3000l/h wavemaker or powerhead Wanted 23 Sep 2016
"Sellathon".....What a awesome weekend ahead!!!!!!! Sponsor Specials 29 Jun 2016
WP25 power head wanted General Discussions and Advice 30 May 2016
DIY to many headaches General Discussions and Advice 9 May 2016