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............Back in 1998, I had a sudden brainwave after trying to work out how better to house Hillstream Loaches in my aquaria. I wanted to give them a more natural environment and trying to provide this with a regular tank setup just didn't work. What they needed for natural conditions was one way flow.....like a river.
To produce the unidirectional flow, I devised a tubular manifold that would draw water through Pond-Pump intake sponges to provide mechanical and biological filtration, and transfer it back to the tank via the Powerheads. This sits under the gravel like a regular Undergravel filter. I had 4 tubes that ran the length of the tank to carry the water in my original design. The extra tubing creates additional routes for the water flow, but more importantly will assist in positioning the structure in the aquarium. By placing heavy decor such as rockwork on top of the tubes, it will be fixed in postion in the aquarium. I have found that a design with just peripheral tubing is very difficult to keep in position, especially if you keep fish that dig in the substrate.This picture shows 3 longitudal tubes.
The tubing is three-quarter inch domestic overflow piping, and is assembled using a special PVC glue. This effectively welds by melting the two joining pieces, and gives about 30 seconds working time before it won't move again, so positioning of components is vital. I test fit everything before final glueing and put reference marks on each part to ensure correct alignment. After 24 hours, this is safe to use once flushed and cleaned in fresh water. A short length of 1" ID flexible plastic tubing is used as an adapter to better link to the conical uplift adapter provided by Aquaclear with the Powerheads that I use. Using various components one can adapt to whatever pump you choose for your application..
I christened my design The River-Tank Manifold.
Here are all the components layed out after cutting, deburring and test fitting in the aquarium.
And at the bottom, fully assembled and just awaiting sponges and powerheads.
Here is an actual built manifold laid out in a 6-foot aquarium.
The size of Powerheads one chooses to run the system depends on what type of fish one wishes to keep. This design can be used for any species of rheophilic fish, but some like more current than others. For Hillstream Loaches, who live in water travelling often at 1 metre/second we can probably never truly acheive such flows in a conventional aquarium. I normally choose Powerheads for these species that combined will move the entire capacity of the tank through themselves a minimum of 12 times per hour. As an example two Aquaclear 802s (now called the Aquaclear 70) will turn over a 65USG tank 13.5 times per hour.
Using 3/4" tubing will have its limitations on flowing much above that kind of flow, but is easily hidden under the substrate. To achieve higher flow rates, the size of the powerheads must increase, plus the diameter of the tubing used. International standards differ slightly, but the next increase in size is to around 1.5" diameter. This would obviously increase the flow capacity to a large degree, but be more difficult to disguise in the aquarium.
Many powerheads feature a venturi effect aeration device built in. This normally operates passively by drawing in air via a tube with adjustable intake, that comes with the powerhead from the manufacturer. To get the main water-flow down close to the bottom-living fish, I mount the pumps far lower than one does normally if using them on an undergravel filter uplift.
This will prevent the passive suction operating. Therefore, I find that a positive air feed from a small diaphragm pump is required.
Using this kind of system with Hillstream Loaches, I found a complete change in their behaviour compared to that seen in a conventional aquarium. They are extremely active and entertaining fish in this environment.
Since 1998, many people all over the world have built themselves their own systems to this design or modified it in some way to suit locally obtainable components. It has been used successfully to breed several species of rheophilic fish other than Hillstream Loaches.
I find this works best the longer the aquarium is. One of its shortfalls is the pumping device. Powerheads provide a strong, but highly concentrated flow. In short aquaria, the concentrated blast will hit the other end of the aquarium and create more back flow than in a longer tank.
This system is low maintenance, requiring only periodic washing of the intake sponges and cleaning of the pumping chamber of the powerheads to maintain performance.
Further reading:
A River Runs Through It
Life In The Fast Lane
Martin Thoene.
Resistance is futile. You will be assimilated.