Sump questions

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Aquarium Advice Apprentice
Sep 2, 2004
Denton, TX
I am VERY new to SW, about one week new in fact. I currently have a 29 gallon FO tank with a Percula Clown. I decided I did not like the 29 gallon after I set it up and went and bought a 40 gallon that is lower, wider and longer than the 29 gallon (36X18X16). It provides far more surface area for gas exchange and evaporative cooling than the 29 gallon, I can use more powerful lights on it and it is lower than the 29 gallon.

I thought I might be able to use the 29 gallon as a sump to add more water volume and to hide some of the equipment. However, I do not understand sumps.

For example, you generally have some sort of overflow into the sump, since mine is an AGA aquarium and not drilled I would have to use something like a hang on the back overflow. The overflow flows into the sump and a return pump inside the sump returns the water.

What if your return pump fails, wouldnt the overflow continue to flow into the sump, eventually overflowing the sump and causing a big mess. What if the reverse happened and the overflow failed somehow. Wouldnt the return pump eventually run dry and pump all the sump volume into the main tank, overflowing the main tank.

Does anyone have a good website or book recommendation that explains sumps in great detail for a newbie like me?
You are exactly correct to be considering the "what happens if..." scenarios. Here's what you do:

There is no need to run the sump water level to full. Keep the sump water level low enough so that water can return into the sump without the sump overflowing. If the pump stops, water will try to flow backwards through the return line. A check valve can stop this flowback, as can a small hole drilled in the return outlet just below the water line. When the return starts to flow backwards, it sucks air into through this hole which breaks the backwards siphon.

Then worry about what happens if the siphon out of the tank stops and water keeps getting pumped into the tank. You can install a float switch somewhere to detect this condition, but fortunately siphons are quite reliable. This is where it is better to have a drilled tank because there is almost no way that a bottom drilled tank can fail.
If you where to look at most of our sumps you would probably think to yourself why dont they put more water in the sump. Well The first concern you have is the exact reason why its not run at full capacity as was mentioned above. The mthod you use to find the max full operating level is to fill the tank to a point just before water goes into the overflow OR to a point just below your sypohon breaks on your return lines. What ever is lower in the water. Then fill your sump to a full level. When you power on the sump the pump will fill the tank the remaning level till the overflow is running. The water level in the sump will drop to a point. At what ever point the water level equilizes in the sump that is your max full operating level. If you power down the pump water will back flow to your sump and stop before it overfills.

Nothign beats seeing a working overflow/sump setup. I know we have many TX members it might be helpful to ask your LFS if they have a working overflow/sump setup you could just look at or if you find another hobbists in your area that has a setup like that you can visit and see how it all goes together.
Here is a pic of my qt tank. I needed to create a larger volume of water, so I used a garbage can, overflow and a return pump. Note that I do not fill the garbage can up all the way. The same principles cound be used for what you want to do,
BTW, its a nice plan. :D
I marked my 20g sump with a "high level" line that I don't exceed with topoffs. That line is the max amount of water that'd stand a power outage before it'd overflow.
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