Advanced Topic Overflow designed to....

Discussion in 'Advanced Topics' started by Nemos Janitor, 3 Feb 2014.

  1. Nemos Janitor

    Nemos Janitor

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    Well we have seen many different designs of overflow contraptions. CTC, slimline, corner boxes, deurso, Bean animal thingy etc. But in this thread I would like to discuss not what is quietest or easiest to install but the overflow style and design that is the most beneficial to the water quality and or tank inhabitants.

    I have some ideas for overflows and would like to throw around ideas for O2 maximization, DOC export to skimmers, Detritus likelihood to surface to overflow. Etc

    Thoughts guys
     
    Last edited: 3 Feb 2014
  2. AdS Guest




    to hide all adverts.
  3. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,163
    Likes Received:
    1,231
    Location:
    Centurion
    Important for me is the linear length of your overflow. Remember that your overflow length and the sump width are directly impacting each other as to the volume it can handle. It is the same volume going over both after all.

    So as not to end up with too much water head in your display, the overflow needs to be at least as long, than your sump width. Longer than sump width is a lot better.

    Too much water head and you drain a lot of water to the sump in case of power outage. So you need to ensure that the sump does have sufficient space to handle that excess water. Plus the likelihood of flushing smaller fish and snails over increases with deeper water heads. Using combs would help, but that just increases the water head more, so now the sump needs to handle more water when return gets switched off.

    The sump can handle more water head. No problem. Would actually sort out a lot of the DSB issues guys have with excess settlement. But you do not want to run more than 5mm head in the display.
     
  4. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    OK let's discuss surface overflows for starters as this is the most common design.

    I am looking for return flow over liner surface area. OD. This could be CTC, corner box, down pipe, gyre extractor or other.

    The above are related mostly to gravity feed filters. Lets look at gravity feed filters first then we will look at force feed filters.
     
    Last edited: 3 Feb 2014
  5. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    @RiaanP the mechanics are one issue. I would like to discuss the biological and filtration aspects.

    Yes you are correct. But the flow over the overflow plays a part......
     
    Last edited by a moderator: 26 Nov 2015
  6. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    Most tank builders and aquariusts build an overflow just based on the volume of water that is to be moved from the DT to the sump. The major consideration is the noise factor. Very little revolves around the circulation of the water within the tank and the speed in which the water flows over the weir.

    In my softy tank for example the slimline weir is in the center back of the tank. The water return enters the tank about 30mm below the water surface on both sides of the back of the tank. Apart from other circulation I have one pump on the right hand side of the tank directed at the water surface about a third of the way to the left.

    The return flow from sump to DT is about 3000lph so that would mean that the flow over the weir would also be 3000lph and that 3000lph of surface water would be skimmed. But is it surface water that is being skimmed? And is it all the surface water that is being skimmed? Apparently not, as there is a oil film that builds up on the surface of the first third of the left hand side of the tank. Now I have tried and installed another pump on the left hand side to "blow" this film which it does, but then the oil and scum is diluted into the water column and remains there as only a very little oil/scum actually go over the overflow.

    Apart from other concerns which I will discuss later what are the thoughts on how to best remove this oil/scum from the tank. Don't point a pump to the surface of the water so that the water surface tension can collect the scum? Or. Disturb the water surface as much as you can so that gas exchange is optimal but oil scum is diluted into the water column causing other water quality issues?
     
  7. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    To illustrate what we are talking about here are two pictures of the same tank. The first pic is the right hand side of the tank showing oil and Scum in the water column. The second pic shows the Scum/Oil on the surface of the left hand side of the tank.

    [​IMG]



    [​IMG]




    From the above it is clear that the water on the left is not skimming the surface where on the right the surface is skimmed or the scum is in the water column. There is definately more contamination in the water on the right compared to the left.
     
  8. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,163
    Likes Received:
    1,231
    Location:
    Centurion
    Last edited: 4 Feb 2014
  9. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    That is correct Riaan. I am using that tank as an example to illustrate how not to build an overflow and the downfalls associated with it. It is a good example.
     
    Last edited: 4 Feb 2014
  10. Visser

    Visser MASA Contributor

    Joined:
    21 Nov 2011
    Posts:
    2,670
    Likes Received:
    45
    Location:
    Willows,Pretoria /Brits
    Very nice subject & question NJ!
    I have experimented with many different overflow & return types in my tanks / frag tanks / sumps...

    My opinion: I hate a tank that doesnt allow proper surface skimming!
    The best overflow i've ever used & seen is the typical skinny overflow (without overflow combs.)
    It allows maximum amount of surface skimmate to be "sucked" from the water surface. Its also important to have the water level inside the overflow to be low enough as the surface skimmate can actually "climb" up the overflow if too shallow.
    Just important to take note that the return mustn't push the surface skimmate away from the overflow, but rather towards. (circular water current towards the overflow.)

    As for return options...
    Still prefer the skinny return option... But with the difference of having a "cover plate" on top of the outlet to "propel" the water at a higher velocity along the surface of the water.
    It creates a much higher surface disturbance, & as a secondary bonus, It causes a very "random" turbulence in the water column.
    For this return to work properly... the outlet needs to "constrict" the flow to allow it to accelerate as it flows into the tank.

    This is the design i'm currently using in my pico, & works fantastic... Even with an extreme return volume. (approximately 40x return volume of DT size.)

    [​IMG]

    [​IMG]
     
    Last edited: 4 Feb 2014
  11. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,163
    Likes Received:
    1,231
    Location:
    Centurion
    the linear length of the overflow is too short. If you take a 5cm space directly around the overflow as the area most likely to be sucked of in the surface skimming action. You do not effectively skim a big surface.

    What is that overflow linear length? If for example 20cm, then you skim the 20 by 5cm directly in front of it, plus a bit to both sides. So 100 square cm directly in front of the overflow. If the overflow was 50cm in length, you will be effectively skim 250 square cm OK, there are a lot more mathematical calculations in it.

    another example will be a dam covered in Hyacinth water plants. Even with the sleuth gates open, only the plants directly in front of the gates are pulled over. The flow also depends on the shape of the dam wall so there are a lot of factors. But it should explain what I'm trying to say.

    With a lot of circular constant water movement you could also end up with a water movement along the front of the overflow that keep things away. Instead of being sucked up and over the overflow. Easy on longer tanks with powerheads pointing down the length of the tank. A longer linear length overflow box could also help here, At least if one side of the tank build up surface scum, the other side do flow out. Surface agitation and a lot more in display water movement to keep things in suspension until it gets sucked out will help as well. Or proper variable wave pumps. (MP40 :whistling:)

    Although the length of your would be the same as a 10 by 10cm corner box overflow. so it should theoretically perform the same. It does not work the same. The corner box is better in cleaning out that side of the surface a lot better due to no cross water flows. Where the center back overflow got sideways cross flows keeping the scum away.
     
    Last edited: 4 Feb 2014
  12. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,163
    Likes Received:
    1,231
    Location:
    Centurion
    The base of Visser's design. His is just a skinny going to the bottom of the tank. This one goes out the back. Same concept. Gives a nice circular surface movement sucking everything away.

    [​IMG]
     
  13. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    Thanks for the input Visser. Some nice design work in there.

    Riaan you are hitting the nail on the head and will work fine on shallow tanks. But what about deep tanks? Should water that is low in O2 and high in nutrients not also be exported to the filter or should one just rely on flow to bring that water to the surface?
     
  14. RiaanP

    RiaanP Moderator

    Joined:
    11 Aug 2008
    Posts:
    23,163
    Likes Received:
    1,231
    Location:
    Centurion
    it should not matter
    With minimum 20 times turnover rate per hour of your display for softies, using powerheads. You should have enough water movement to move oxygen starving water from the bottom of the tank to the top, unless you got a diving pool. For SPS and using 60 or even 80 times turnover. You should be able to keep things in suspension until they flush over the overflow.

    But again, with wavepumps and depending on your settings, you have to calculate the real turnover rate. Not the theoretical rate. Having 2 Vortech MP40 pumps running at long interval mode. Means that you only have a turnover of 15000L/h and not the theoretical 30000 if both pumps run full blast. A lot easier to work out the turnover with non-controllable powerheads.
     
    Last edited: 4 Feb 2014
  15. Visser

    Visser MASA Contributor

    Joined:
    21 Nov 2011
    Posts:
    2,670
    Likes Received:
    45
    Location:
    Willows,Pretoria /Brits
    How deep are you talking about here?
    For any tank shallower than 1200mm, I dont believe you will ever have anywhere in the tank with a higher / lower oxygen or nitrate levels.
    That is the wonderfull part of Diffusion... Oxygen (or carbon dioxide) & nitrates will (with the help of diffusion), mix with the "shallower" water in the tank until it reaches the surface.

    The thing about a reef tank is that due to the #1 rule in reefkeeping... Is always to have enough flow (turnover from sump, & flow from wavemakers). So even if there isnt any other method for the mentioned elements to reach the surface... The flow should do the job.
     
  16. Nemos Janitor

    Nemos Janitor Thread Starter

    Joined:
    7 Feb 2009
    Posts:
    8,384
    Likes Received:
    286
    Location:
    Joe's Mountain
    Hmmm...I have noticed that the tank in this example which has a 750mm water height. Has a lower Redox at the bottom of the tank compared to the top of the tank. I will hook up the HI 9828 and take some readings tomorrow.
     
Recent Posts

Loading...
Similar Threads - Overflow designed Forum Date
Overflowing skimmer Curve7 - 2 days Protein Skimmers, Mechanical Filtration Tuesday at 11:35
Overflow fitting help please Pumps and Waterflow 30 Nov 2016
Drilling and overflow HELP Beginner Discussions 21 Oct 2016
Can you make a algae scrubber in your overflow? Anything DIY Related 25 Sep 2016
[wtd] Overflow box Wanted 3 Aug 2016
Overflow cover up General Discussions and Advice 2 Aug 2016
Plexiglas overflow Anything DIY Related 19 Jul 2016