# How do overflows work?



## Gizmo (Dec 6, 2010)

I've seen them, but I don't know how they work or why they are needed in things like sump and canister setups. Can anybody fill me in?


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## mec102778 (Feb 17, 2011)

I think the overflow is the alternative to using a siphon, while a siphon continues to draw water until the siphon breaks. An overflow is directly related to the pump you run to move water from refugium/sump/resivoir back to the main tank. The overflow also acts as a skimmer helping to create a constant water surface change to allow better O2 exchange.


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## mec102778 (Feb 17, 2011)

Ok sorry I don't think I answered your question.


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## Gizmo (Dec 6, 2010)

Gotcha. So if you're injecting CO2, overflows are less desirable.


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## mec102778 (Feb 17, 2011)

I don't believe so, overflows work as a means for filtering the tank. Even while injecting CO2 you would still run your skimmer or filter. I'm not a good person to explain this. I understand how it works but not the "why". If I'm not mistaken some people use the overflow/refugium/pump/tank system so they can monitor the water level in the refug and just top that off as needed. But the refug also give a place to filter/heat/add chemicals etc.. without adding the directly to the tank.


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## beaslbob (May 29, 2009)

[email protected] said:


> I've seen them, but I don't know how they work or why they are needed in things like sump and canister setups. Can anybody fill me in?


Overflows are NOT needed in totally closed system like canister filters. If the canister is below the tank and working and the power goes out, all that happens is the water stop circulating through the canister is all.

But with an open system like a sump, the tank would continue draining untill some how it stopped. The overflow is designed to stop before "woopsies".


A good example of an overflow is found on your sinks/tubs. It's the little bitty hole near the top. So if you plug the drain a leave the water running, the water rises up to that hole the "overflows" thorugh that hole down the drain.

So only our tanks with sumps we setup an overflow to do the same thing. So that as the return pump pumps water to the higher container, the higher container water level rises untill it overflows down the "overflow" and maintains the higher container's level.

It's more complicated but that's the basic idea. And an overflow can be made from $20 of pvc and does not require drilling holes.

to set it up get it running then:

1) cut power --- see if the upper container stops at some level without flooding the lower container

2) restore power---- is if normal operation returns.


3) fail (break siphon, plug) the overflow.-----see is sump runs out of water before upper container floods.


Once you set one up and get it running it makes more sense. But it can be confusing at first.

my .02


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## Gizmo (Dec 6, 2010)

beaslbob said:


> 3) fail (break siphon, plug) the overflow.-----see is sump runs out of water before upper container floods.


Thanks for the info bob  By the upper container flooding, do you mean the tank itself? Or the overflow container? Or the upper container of the sump?

And I've heard many arguments for or against the use of sumps with injected CO2 as the overflow and other factors contribute to gassing the water out. Thoughts?


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## beaslbob (May 29, 2009)

[email protected] said:


> Thanks for the info bob  By the upper container flooding, do you mean the tank itself? Or the overflow container? Or the upper container of the sump?


No I mean the upper container *old dude

There is a method to my madness. The sump by definition is the lowest container where the water is pumped to the highest container. Which then drains (either directly or through other containers) to the sump.

In some setups there is a container actually above the tank. Which can be a refugium, container filters or whatever. In that case the tank itself is the sump where water is pumped up to the refugium/filter container above the tank.


[email protected] said:


> And I've heard many arguments for or against the use of sumps with injected CO2 as the overflow and other factors contribute to gassing the water out. Thoughts?


Let me give a shocking idea. In a tank balanced out with plant life, that tank could be totally sealed and the fish and plants do just fine. The plants suck out the carbon dioxide from the fish and also return oxygen for the fish.

some inject co2 for the plants sure. And in tanks totally devoid of plant life sure air gas excahnge is important. 

But IME planted tanks need none of that and the plants trump everything else.

the main advantage of sump system is that they hide stuff instead of all the "stuff" hanging off the display. 

An important second consideration is refugiums. The refugium can be a third container that drains to the sump but is not part of the tank. There you can grow algae, plants, various critters, and so on away from the preditors in the tank. A very common setup with marine tanks where the fish eat the plant life (macro algaes). Plus the critters (pods) thrive in the refugium provide food for some fish also.

Algae truf scrubbers (where algae and cyano are grown on screens in a seperate container) is another example. Obvously it is much better to grow ugly algaes there then in the tank iteslf.

Finally, in very large systems you may want the sump in another room or basement just to make maintenance easier. There you can do water changes, change filter media, dose stuff and so on away from the display area which could be in the living room for instance.

The down side is that sump system are more complicated to setup and operate and therefore prone to failures.

One thing I did on my 55g marine tank was partition the back 3" so that formed a refugium. Macros and pods thrived in that section, nitrates and phosphates dropped to unmeasureable levels, fish that ate macros grazied all day on the macros the poked through the partition. And it only cost me $10 for the egg crate partition plus a couple of $9 utility fixtures.

Of course there was none of the failure modes a sump system had either.

(as I found out later when I added a sump. *r2)


my .02


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## jrman83 (Jul 9, 2010)

He means the tank.

If set right and an overflow box is used, at least the ones available now, I don't see how the main tank can over flow. I tried to make it happen to mine. You set the level the overflow is under the tank's water level. It will flow into that box until the exiting water from the tank (to the sump) cause the box to now be above the water level of the tank. Flow then stops...at least from the overflow. The water is then returned by a pump that sits in the sump. The resulting water returning to the tank raises the water level above the level of the overflow box and flow resumes, or continues. You would set it where it is continuous and no breaks in flow. The return line is another area of concern to break the siphon. It is a hose going in your tank. Most return nozzles have a pin-hole in them that causes the siphon to be broken once the pin-hole is above the water level of the tank.

As far as maintaining a particular CO2 level....when the water is sent from the overflow box down to your sump or wet/dry there is a lot of interaction with the atmosphere and if that period is too long the gas can escape the system, unless you make it somewhat air-tight, which I found nearly impossible. I would start injecting my CO2 and watch the ph go down nearly a full point, kick on the wet/dry and then watch it raise that full point. I sealed it and the only thing it did was to increase the amount of time the gas-off occured from about 4hrs to 12-16hrs. Anyone using one and CO2 together and telling you they aren't gassing off their CO2 is probably not totally correct. They may be able to maintain a 30ppm CO2 level, but they are doing this using the ph/kh/CO2 relationship chart. Since the only way to check the true level of CO2 gas in your tank, that I'm aware of, is taking ph sample of removed water and then checking again in 24hrs, the results I got from that test made me remove my wet/dry. I got the Eheim wet/dry canister which doesn't gas off the CO2 since the system has to be air tight.

Tom Barr is the only one I know who seems to have success with it. He is the one I suggested to seal mine and this is how he does his, I assume.


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## beaslbob (May 29, 2009)

FWIW here is thread I did a long time ago with a pvc overflow design.


http://www.aquariumforum.com/f37/pvc-overflow-3492.html

JR: if the overflow "breaks siphon" of plugs then the return pump can flood the upper container (usually the tank). the adjustment is to remove water from the sump or raise the pump intake so it runs dry before the flood.

JR also pointed out that any closed pipe/tube can be a siphon. The under power out the return lines will be siphons and drain the tank untill the sippon breaks. Hence little holes to suck air and break siphon or even just having the return outlets above the water level.

my .02


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## jrman83 (Jul 9, 2010)

Yeah, I can see where the could happen. Hopefully the only time that would happen would be during a power loss (which breaks the siphon on the overflow I used) which would kill the return flow also though.


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## Gizmo (Dec 6, 2010)

I'm fascinated with sumps - always have been. I see that gassing out is a natural by-product of sumps, that refugiums are awesome, and other benefits of sumps, and I also see their complications and complexities and I'm intrigued. So sorry for pestering, but I'm going to ask a few more questions...

@bob - so I'm interpreting what you're saying as in there's an upper container separate from the sump which many use as a refugium, and you want this container to drain before the sump empties or the tank overflows if the overflow box is blocked, correct? If so, what's to prevent the pump from burning up once it's running dry?

Also, where exactly are the pumps for sumps? Are they in-line with the inlet or the return, or are they in between compartments in the sump, or are they at the sump end of the inlet? I would guess in-line with the return, but I could be wrong.

@Ben - I'm a little confused by the necessity of a siphon action on the return - isn't the water being "pushed" from the sump into the tank? How does a siphon work going from the sump back up to the tank on top of it?

Obviously this is gonna be way too much of a hassle for my 29 gallon, but I forsee potentially acquiring a 75 gallon in the near future, at which time I will be getting a sump going.


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## jrman83 (Jul 9, 2010)

[email protected] said:


> Also, where exactly are the pumps for sumps? Are they in-line with the inlet or the return, or are they in between compartments in the sump, or are they at the sump end of the inlet? I would guess in-line with the return, but I could be wrong.
> 
> @Ben - I'm a little confused by the necessity of a siphon action on the return - isn't the water being "pushed" from the sump into the tank? How does a siphon work going from the sump back up to the tank on top of it?
> 
> Obviously this is gonna be way too much of a hassle for my 29 gallon, but I forsee potentially acquiring a 75 gallon in the near future, at which time I will be getting a sump going.


The pumps sit in the area of the sump or wet/dry filter that is usually after some form of filtration has occured - so the cleanest the water is going to get before being returned. The pump is directly connected to the return line and the pump just free flows surrounding water into in that rests in the bottom of the sump/filter. In a standard wet/dry filter, the water comes down from the main tank, hits some form of fibrous filter, water goes into something that is like pouring water into a drawer that has holes all in the bottom of it, the water drips down through plastic bio-balls, then collects in the bottom and then some have a last form of filtertaion before the water is available to be pumped out. Usually in the sump or wet/dry there will two sections. One of the sections would be considered the filter section (bio/mechanical) and the other section would have the pump. 

There is no necessity for there to be any siphoning action on the return line. But as you know, anything (tube/hose/airline/etc) can be a siphon once solid flow is in that tube, no matter which direction the flow is occuring. When the pump is running and the nozzle (on the other end of the hose) is below the water level of your tank there is no break in the water. Therefore, if the pump stops pumping for some reason, the flow can now reverse and flow water out of your tank. A pin-hole in the nozzle breaks this siphon once the water drops enough to have that pin-hole exposed to the air.


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## beaslbob (May 29, 2009)

[email protected] said:


> I'm fascinated with sumps - always have been. I see that gassing out is a natural by-product of sumps, that refugiums are awesome, and other benefits of sumps, and I also see their complications and complexities and I'm intrigued. So sorry for pestering, but I'm going to ask a few more questions...
> 
> @bob - so I'm interpreting what you're saying as in there's an upper container separate from the sump which many use as a refugium, and you want this container to drain before the sump empties or the tank overflows if the overflow box is blocked, correct? If so, what's to prevent the pump from burning up once it's running dry?


It could. Hopefully that doesn't happen all that often. The only difference actually is whether or not the display floods before the pump runs dry. 

That said some put a float switch to turn the pump off if the upper container rises above a certain level. More complexity and if that switch directly goes to 120vac a big shock hazard. When I went away for more then a couple of days I just turned off the sump.



The sequence is upper container (tank) drains to intermetiate container (refugum) drains to sump. water is pumped from sump to upper cotainer. 



[email protected] said:


> Also, where exactly are the pumps for sumps? Are they in-line with the inlet or the return, or are they in between compartments in the sump, or are they at the sump end of the inlet? I would guess in-line with the return, but I could be wrong.


they pump water from the sump with the output inline with the return lines.



[email protected] said:


> @Ben - I'm a little confused by the necessity of a siphon action on the return - isn't the water being "pushed" from the sump into the tank? How does a siphon work going from the sump back up to the tank on top of it?


with power on the return lines are full of water being returned to the tank. If the outlets are below the water level and the pump turns off, the return pipes will form a siphon through the pump back to the sump. If you don't break that siphon the return lines will drain until the end of the return lines is above the water remaining in the tank.



[email protected] said:


> Obviously this is gonna be way too much of a hassle for my 29 gallon, but I forsee potentially acquiring a 75 gallon in the near future, at which time I will be getting a sump going.



Keep in mind this does not have to be all that expensive except for the pump. Pvc pipe and a couple of plastic storage container would be fine.

also keep in mind as you automate it that an ATO can sense a low sump level from a plugged drain as well as evaporation. So can pump more water to cause a flood during a drain failure. Better to use a drip system.


my .02


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## Donald Hansen (Jan 21, 2011)

Ladybower Dam - Video

Here's a video of a really big overflow.


DLH


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## Gizmo (Dec 6, 2010)

Thanks guys! I think I've got it down. Let me see if this makes sense...

Starting from the tank, as water is pumped back into the tank the water level rises, spills into the overflow, and drains down to the upper compartment of the sump, which can be filtration or a refugium. Water then falls into the lower compartments, through filtration, then is pumped out back up into the tank.

If the overflow clogs, water is pumped out of the sump into the tank until a level sensor triggers the pump to shut off or the sump is dried out completely.

If the pump fails (power outage or otherwise), the return outlet being above the water level in the tank OR a pinhole above the level will break the reverse-siphoning action to prevent your sump from overflowing.

In-line items like reactors, heaters, etc. can be incorporated after the pump, pH meters can be incorporated into the sump itself.

PVC & acrylic sheeting or plastic tubs, with sealant, are the best/cheapest items for a sump.

Now I'm addicted to a new thing. I will have a sump one day!

Last question - how do you accurately fill a sump/tank setup to the correct level, and how do you do a partial water change without screwing things up?


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## beaslbob (May 29, 2009)

[email protected] said:


> ...
> 
> Last question - how do you accurately fill a sump/tank setup to the correct level, and how do you do a partial water change without screwing things up?


I think you got the basics down.

You determine the correct level by doing all these tests and adjusting the levels to prevent floods. Then get the system running normally and mark the water level in the sump. And never fill the sump above that mark.


On water changes you could just trun off the system and do a water change as normal.

Or plumb it so that say the drain line goes to a drain instead of the sump while adding new water to the sump.

You can also use the sump for dosing such as the diy 3 part system also.


my .02


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## WhiteGloveAquatics (Sep 3, 2009)

If its a wet dry, you fill the sump and keep the level at or just below the biomedia. The bacteria in a wet/dry needs oxygen to do its job. 

I use a overflow that has a continious siphon, power goes out, so does my overflow, power kicks on, it comes back on.


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