# Will a PVC Overflow work with low water level?



## scooter64 (Aug 9, 2011)

I am starting work on converting my 75g aquarium to a paludarium and have opted to use a sump for my heaters and water filtration with the return to supply 2 separate water features. I cannot drill my tank as I initially wanted because there is a sticker on the bottom of the tank that says ALL panels are tempered glass DO NOT DRILL!.. So I put together a DIY PVC overflow just like this one










I'm a little worried that this may not work very well in a setup where there will only be 3" of water. I'm not to a point yet where I can fill and test it, but was wondering if any of you have had success with an overflow such as this in a low water setup? I sure hope so, because I already bought the sump and return pump  Thanks!!


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## JoshsDragonz (Jun 30, 2012)

I haven't used this style myself even though I know it works good in an aquarium. It's a basic siphon system that keeps it's self primed if the water level drops below the inlet. The only problem with having the inlet pipe so short could be it pulls air and breaks the siphon. So as long as its able to be primed and not pull air, I would think it would work. It's worth a try, especially if you can't drill. 

-Josh


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## Pumilo (Sep 4, 2010)

Bubbles will collect in the tube. Bubbles collect in an aquarium overflow, too. On an aquarium overflow box, it is easy to see the bubbles and you can increase the flow rate until you see the bubbles being carried all the way down the tube with the water, until it exits the overflow setup. 
Your potential problem here is how far the bubbles have to travel to get down and out of the tubing. Plus, you cannot see the bubbles due to the use of PVC.
I'm not saying it will not work, just pointing out the potential pitfalls.
The flow rate would probably have to be fairly high in order to carry all the bubbles out of the tube. Too many bubbles in the tube will break the siphon. If you try to run the system slower, then dissolved air in the water will eventually allow air to build up and break the siphon. If the siphon breaks, your land mass could flood and drown your frogs.


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## JoshsDragonz (Jun 30, 2012)

Hey Pumilo, I do believe that this style of overflow is meant not to flood. The only amount of water that should return to the tank is the portion in the pipe up to the taller pipe meant to break the siphon when the water stops flowing.

-Josh


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## scooter64 (Aug 9, 2011)

Ouch.. Fears confirmed. I am using a 20 Gal sump, so if I test this out and it appears to work, I am certainly going to implement a float switch in the sump so that if my siphon fails, it will stop the return pump from flooding out my land mass. Sound feasible? If not, I'll need to abandon the sump idea I guess..


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## Pumilo (Sep 4, 2010)

JoshsDragonz said:


> Hey Pumilo, I do believe that this style of overflow is meant not to flood. The only amount of water that should return to the tank is the portion in the pipe up to the taller pipe meant to break the siphon when the water stops flowing.
> 
> -Josh


I do believe you are right. I haven't used that style myself, but looking at it again, I see how it would be self priming now, but I'm not sure if it will work as a low level system. It doesn't look like the system will start to flow until the tank is almost full.


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## scooter64 (Aug 9, 2011)

JoshsDragonz said:


> Hey Pumilo, I do believe that this style of overflow is meant not to flood. The only amount of water that should return to the tank is the portion in the pipe up to the taller pipe meant to break the siphon when the water stops flowing.
> 
> -Josh


I believe that if the siphon were to break, my return pump would still be pumping about 20 gallons of water to the display tank (without some type of failsafe in place) ..Very bad..


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## JoshsDragonz (Jun 30, 2012)

scooter64 said:


> I believe that if the siphon were to break, my return pump would still be pumping about 20 gallons of water to the display tank (without some type of failsafe in place) ..Very bad..


Yea I agree on this... I had't thought about the volume of water in the sump. That style of overflow is designed to start flowing when the water in the main tank reaches the inlet level again... Well that's with the stand pipe at a taller level though. If you can use a float switch to shut off the return pump as a back up I would. In the end if you have the funds to build it and the time to give it a thorough testing it would at least give it a try. (Without any inhabitant's in the tank  ).


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## scooter64 (Aug 9, 2011)

Pumilo said:


> I do believe you are right. I haven't used that style myself, but looking at it again, I see how it would be self priming now, but I'm not sure if it will work as a low level system. It doesn't look like the system will start to flow until the tank is almost full.


The picture I used is strictly for reference. My intake tube will be cut to a height to maintain a 3" water level. I planned on placing a check valve on top to get the initial prime going and then after some googling I found this video that uses an "aqualifter" pump to maintain the prime. I wonder if this would help?


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## JoshsDragonz (Jun 30, 2012)

That would be a nice add-on safety feature.


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## Pumilo (Sep 4, 2010)

If you need an aqualifter, it is a mistake. I had a high flow style overflow box once that required an aqualifter. Eventually, the aqualifter failed as every pump will eventually, and my system lost prime and flooded.
In my case, the aqualifter ran constantly to remove any built up air bubbles. It was an effort by the manufacturer to be able to use the overflow in conjunction with a somewhat smaller pump. Problem is, the aqualifter must eventually fail. When it does, bubbles build up, possibly very quickly. Once enough bubbles enter the overflow, the siphon breaks and the system fails.


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## scooter64 (Aug 9, 2011)

Agreed. Last night I was able to crudely put all the pieces together and test out this thing. It started to work fine, but repeatedly kept failing. I need to ditch this plan and rethink this thing. The risk is just too much for me to keep going in this direction. Now it appears I may also have a 20g sump to convert to a viv as well


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## kitcolebay (Apr 7, 2012)

I had originally planned on using a sump system for my 150 setup. Unfortunately, I couldn't get my tank drilled either. I switched to a canister filter instead and placed the inlet at the bottom of the false bottom with the outlet mounted at the top of the waterfall. You lose a little bit of height, but so far it has been working great.


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## scooter64 (Aug 9, 2011)

Thanks. I should have read this before I just posted a new thread asking for filter advice!!


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## Pumilo (Sep 4, 2010)

I just want to toss this out there. It's extremely rare to have a tank with tempered front, side, and back panes. If the back were standard, annealed glass, you could drill the back pane. Here is a method of detecting tempered glass. How to tell if glass is tempered.


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## scooter64 (Aug 9, 2011)

Thanks Pumilo, that is a great tip. I'll give this a try tonight to make sure. I thought it was strange too because I thought normally just the bottom would be tempered, but the sticker does indicate that all panels are tempered. For the life of me I cannot recall the manufacturer, but the tank came from petsmart quite a few years ago..


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## Pumilo (Sep 4, 2010)

When you temper glass, it also adds visual distortion to the glass. This is why it is generally NOT used except for the bottom panel.


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## scooter64 (Aug 9, 2011)

Pumilo, I did the test tonight and it seems to me that the back glass is really not tempered. What do you think? Here's the video of the test. Sorry for the crude editing, I am not too good with videos...


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## JoshsDragonz (Jun 30, 2012)

From the vid the back looks different than the bottom pane for sure. But I have never used this method, so I will let Doug give his opinion.

-Josh


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