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The key to a good aquarium overflow design is ensuring that water flow is as silent as possible. An aquarium overflow does exactly what it sounds like, it allows water to overflow out of the tank. The primary purpose for this is to route tank water to a sump to house your equipment out of sight, however that is just one of the benefits.
In an external overflow water to rises over the rim of your aquarium. It then drains down a pipe to your sump. In general, external overflows are less ideal. They can fail much more easily and when they do fail they can easily lead to tank water overflowing your aquarium and onto the floor. That said, many reefers have great success with them and appreciate the lower cost and the lack of need to drill through the tank wall or bottom.
Internal overflows are a little more daunting since they require drilling the aquarium or purchasing a predrilled aquarium. The benefit is a much more reliable overflow solution. It is also a much cleaner looking setup.
External overflows are naturally quiet due to the siphon required to flow water over the aquarium rim. Internal overflows can be noisy as the basic design has a standard open pipe that gurgles. There are designs that address this problem. There are three popular internal overflow designs that address the noise issue in different ways.
These overflows are named after their designers, hence the somewhat unusual names. Let’s review each overflow design.
The basic premise of the Durso design is to submerge the inlet and add an exposed air inlet above the water surface to reduce noise. Sometimes a valve is included on the air inlet to better tune the overflow. The drain pipe exit is placed below the waterline in the sump so there would be no splashing noises.
The Herbie design attempts to go silent the same way the external overflow does, by going full siphon. To do this your return pump needs to be matched precisely to the flow ability of the drain pipe. Flow is matched by incorporating a valve in a drain pipe. The valve can be adjusted to limit the flow to match that of the pump. This design also includes a second normal drain standpipe as an emergency drain in the event the primary were to become clogged in some way. While the main drain pipe exit is placed below the waterline like in the Durso design, the emergency is not. This is so that it would make a prominent noise to alert you to a problem with the primary drain.
This design is a combination of the Durso and Herbie Overflows and includes all three drain pipes. One Durso Style as well as both Herbie drain pipes. The main Herbie drain is tuned to go full siphon but allow an additional amount of water to drain down the Durso drain pipe. The amount allowed to drain down the Durso pipe is just enough to allow it to adhere to the walls of the drain. These prevents any chance of gurgling and gives more latitude for fluctuations in flow without failing over to the emergency overflow.
The most silent and bulletproof solution for an aquarium overflow is the Bean Animal Internal Overflow. Some may consider it overkill. When it comes to my aquarium however, this is my preferred method. I feel you can never be too safe. Especially when it comes to preventing water overflowing onto the floor in my home. There are many other solutions to the internal overflow option but these three rise above the rest. Hopefully you’re now well informed on overflow function and design for your own reef tank.
Next consider reading Aquarium In-Sump Refugium Facts & Benefits to learn more about what comes next after the return plumbing. Good luck and happy reefing.
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