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Old 02-27-2010, 03:36 PM   #1
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Post General overflow questions. (Weir content as well)

I searched, and most of the threads on here are old and the pictures no longer work, so I figured I'd simply make my own thread.

I have some quick questions on making a weir, based on this website.
DIY Overflow Box

Online calculators/overflow drain size:
First, are there any online calculators out there for how big you should make these things for certain tanks? Or at least for how big the drain should be? (Ok I found some calculators on, I'm not sure if I should like this site here but... Reef Central Online Community) Also, using the calculator for "overflow drain size", it gives an answer of "linear overflow size." From what I've read, does this mean that, for the type of weir I want to build, it'd be the dimensions of the "box" that is under the water? Aka if I came up with a linear overflow size of 10inches, my dimensions of my inner box COULD be 6x2. So six inches long and 2 inches on each side, adding up to 10 inches? Does the depth of the box have anything at all to do with this? OR, does it mean that if I added the height of the intake of the weir, plus the upside down U bend, plus the thing on the output to keep the siphon? I'm so confused...

Turnover rate:
EDIT: After more searching, I've found this to be a highly debated topic, depending on a lot of factors. These include power filter or sump/refug, what types of fish, SW or FW, etc etc. How do you know what kind of currents your fish needs?
I know there is an optimal "turnover" rate (For example, all of the water in the tank is filtered 2 times per hour.) for certain tanks, but all I can find is this.
Filter Turnover Rate or Water Turnover Rate

So according to a post in there, 8-10 is good for a fish only SW tank? I'm guessing that means that all of the water should be filtered 8-10 times per hour? Seems like a lot...?? Are these numbers the same for a FW tank?

So let's say (hypothetically) I have a pump from a sump that ACTUALLY pumps 200 GPH into a 20 gallon tank, and I have an overflow that can easily keep up with it. (Of course, the pump would be rated higher as to account for overhead and filter stuff, and there would be other factors, but this is all hypothetical). That would mean that all of the water in the tank get's filtered 10 times per hour? Correct?

Air tube in weir?:
OK, next question. Based on the designs for the weir above, there is a small tube in the top most section of the weir, to draw out air and keep the siphon. Now, people say this is attached to a powerhead. From what I understand, a powerhead is simply something that takes in water, and pumps out water. They are useful if you want to create currents, or you can attach them to UGF tubes instead of using airstones. Now, if I am correct... where the HECK do you connect an air line to one of these things? While yes, it would probably suck the AIR from the top of the weir, but wouldn't it also suck the WATER from it? Then this would cause it to LOSE siphon? Then again if the power went out so would the powerhead... therefore you wouldn't have a chance to lose siphon then, but you see my point.

Oh, and I like to build things by myself. Mainly because I can, and I can usually do it cheaper than buying one. So please don't come in here just to say "Go buy one from so and so a store." If it comes to that, I'll do the appropriate research and go buy one, but as of now, I want to learn how to build on.

I think those are all of my questions for now... I'll be back later!!! And thanks in advance. I'm not building a sump or anything right now, I just want to be educated so that when I DO decide to build one, I'll have the knowledge to do it.

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Old 02-27-2010, 05:04 PM   #2
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A good rate of flow thru a sump is 5x-10x the tanks total water volume.

That design does work, but I personally do not like it. It's based on the CRP style overflow. I like the u tube style much better and they don't need the pump to draw out the air. I used a u tube style overflow for over 15 yrs and never had an issue with it.

I'm all for DIY and most of my system I built myself. I would suggest you look at some retail u-tube style overflows and base your design on that. These give some measurements. Overflow Boxes | Wet/Dry Aquarium Filters | Filters | Aquarium - ThatPetPlace.com I also still have mine and can take pics and measurements for you if you want to go that path.

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Old 03-06-2010, 11:40 PM   #3
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I agree. My U-tube has been working perfectly. I built it all myself. Still need a few adjustments but let me know and I will show you pics and explain how I built it. Very simple, very cheap and you can build it all yoursef, if your interested.
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flow, overflow, weir

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