Overflow rate vs. Return Rate... + Tank Circulation

Discussion in 'Tank Talk' started by Ochopus, Jul 17, 2007.

  1. Ochopus

    Ochopus Cuttlefish Registered

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    Hello Everyone!

    So, after days and days of researching, I finally plunked down some $$$ and bought a 50 gallon acrylic tank, stand, top, and a 30 gallon sump with wet/dry trickle filter, room for a skimmer and return pump, as well as a refugium on the other side... I'm taking a lot of ideas from Marc's super sump found here: http://www.melevsreef.com/55g/55sump.html

    I have to fashion some baffles for my sump... but everything else I kinda bought pre-made. If anything can go wrong, I'm your man, so I figured it would be best not to test my mad crafting skills on a brand new acrylic tank and mess it all up! I also have to ceph proof the HOB overflow, but I think I could handle that as everthing is a pretty tight fit. Here are some pictures...


    Back of tank:
    [​IMG]


    Top view of overflow:
    [​IMG]


    Here you can see the top of the overflow box touches the tank lid, so I am thinking of glueing them together and then closing off the ends with two flat pieces of acrylic:
    [​IMG]


    Anyway... with all that said :razz: ... I have a few questions...

    :confused: 1) Can an overflow placed at water level drain too much or too fast? The one I have (shown above) seems large.

    :confused: 2) How do I figure out flow rates for the overflow and return pump? I thought I read 300 gph if overflowing from water level.

    :confused: 3) How do I know how strong of a return pump/flow I will need? Should it match the rate of the overflow??

    :confused: 4) The water from the return pump, it provides the main tank circulation correct? So, should I run a return line to each top corner of the tank (for a total of two)?? And aim the water flow diagonally to meet in the front lower middle of the tank? (Did'cha get that?!)

    :confused: 5) What should I use on the end of the return flow lines? Spray bars? Those flat open mouth looking nozzles?


    Im so excited and anxious to start cycling since I know I'm still at least 3 months away from buying my first octopus!!

    Thanks in advance for your help and answers!

    ~Marc
     
  2. Animal Mother

    Animal Mother Architeuthis Supporter

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    Your link is type-o'd

    Marc does great work. I'm going to have him build an internal overflow box that's octoproof for my next octopus tank.

    I think his site is a must for DYI'ers personally.

    www.melevsreef.com
     
  3. Thales

    Thales Colossal Squid Staff Member Moderator

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    Hi - assuming I understand your questions correctly: :grin:

    An overflow should only overflow water at a speed equal to the water that is being pumped into the tank. In a power outage it will drain to the point where it cannot drain anymore (the bottom level of the teeth on the internal section).

    Best to see if you can find a reference to how much water a 1 inch 'u' tube will pass and double it because you have two.

    IMO you want to match the rate of flow though the sump with the rate the skimmer processes water. What is usually a limiting factor is the amount of water an overflow will pass through the teeth. Yours seems pretty wide and pretty big, so I don't see much of a problem.

    Sounds like a decent way to go for an octo.

    Or nothing! :smile: Its really personal preference.

    RR
     
  4. Animal Mother

    Animal Mother Architeuthis Supporter

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    Oh yeah, and cool setup! Congrats on your new tank! :)
     
  5. Paradox

    Paradox Haliphron Atlanticus Supporter

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    Hello Marc, I think most of your questions can be answered with the fact that the rate in which you overflow will go will automatically match the rate in which water is being pumped into the tank. That is unless the amount of water is pumped in faster then the maximum rate the overflow is designed to handle.

    Also, the water level in the tank will be determined by the height of your overflow. As the tank is filled with water, it will drain into the overflow and the water level balances at this point.

    The strength of your return pump is dependant on your tank design. How high the water is being pumped, how many splits or elbows etc will all reduce the gph of a pump. A calculator for this can be found at reef central here http://reefcentral.com/calc/hlc2.php

    Flow is very important in a tank for if designed properly, it will allow you less time cleaning the tank. The more dead spots in the tank, the more detritus build up. You wont need anything as crazy as a reef setup, but it would be a good idea to use two returns, so youll need less powerheads and other circulating pumps. You can even use wave devices or a scwd to get more variation in flow.

    For a 50 gallon tank, I would personally get a pump that will still reach 500-600 gph once entering the tank. This will probably be a pump that can do 700-800.

    Also, your overflow does not look octoproof. You will need to cover the slits with a mesh such as window screen material or a gutter guard.

    Hope that helps!
     
  6. DHyslop

    DHyslop Architeuthis Supporter

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    As a supplement to Thales' excellent reply, I'd like to mention that it is possible to have too big of an overflow. The more water your pump is moving, the faster water is moving through the u-tubes in the overflow. The faster that movement, the less likely it is for bubbles to get trapped in the tube because more of them will be entrained in the flow and come out into the external box. If the water is moving slowly, bubbles might accumulate at the top of the bend: if that bubble grows too big the siphon could stop and the tank may overflow.

    I believe the rule of thumb is a 1" ID u-tube will handle about 600 GPH and two of these u-tubes will handle 1200 GPH. If you have considerably less than 600 GPH, you may be worried that the water is moving slowly through the tubes, and an easy solution would be to simply remove one of them. As always your mileage may vary, and every overflow should get a quick daily inspection, just to be safe.

    Good luck,

    Dan
     
  7. Thales

    Thales Colossal Squid Staff Member Moderator

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    Great points Dan!

    I have never used an HOB overflow that didn't have a built in air vent, or a DIY air vent. The idea is to be able to vent any air that may collect at the top of the U-Tube causing the siphon to stop. An airline sized nipple is glued into the the highest point of the u-tube and something like an aqualifter pump is put on the nipple. The aqualifer will suck all the air out of the u-tube and continue to suck a small amount of water through the u-tube and that water is routed back to the tank. IMO, such a device is a necessity for the type of overflow you are using because it cots about 25 dollars to DIY and will save your tank from overflowing at some point.

    I currently run two similar overflows, both with aqualifters and they still make me nervous. As soon as I have the chance (IE when the inhabitants of the tanks are no more) I am going to drill the tanks and remove the HOB overflows.

    Some people have had long term excellent results with such overflows, they just make me nervous. :grin:
     
  8. DHyslop

    DHyslop Architeuthis Supporter

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    To be honest I would be more comfortable running a U-tube overflow without such a mod. Drilling a hole in the tube and cementing in a nipple adds more fault modes: the tube might crack from the joint, the joint itself might crack or separate, or the air hose might simply come off the nipple. From an engineering standpoint, I believe this setup has less fault tolerance but I know there are many people who run overflows with Aqualifters (great little pumps!) successfully.

    Bottom line: nothing is foolproof or maintenance free, even drilled overflows/Megaflows. Take a quick look every day, and be ready to clean as necessary.

    Dan
     
  9. mosthated

    mosthated GPO Supporter

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  10. DHyslop

    DHyslop Architeuthis Supporter

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    I fail to see how that will remove air bubbles?
     
  11. Thales

    Thales Colossal Squid Staff Member Moderator

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    Is that the right link? The link above is for a check valve which will not remove air from the u-tube.
     

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