Along with a past experience with keeping a stream biotope tank, two recent, reasonably unrelated experiences have given me an idea for a stream tank which I've never seen the like of before. I once kept a school of a dozen Rainbow Shiners, a few Rainbow Darters, and a couple of Cambarellus schuhfeldti in a 30 gal tank which had a 2600 gph SEIO circulation pump on it. The Shiners in particular truly seemed to enjoy the insane amount of flow exhibited really intense schooling behavior. But the flow was like a Jacuzzi, going off in all directions. Recently a day behind the scenes at the Adventure Aquarium introduced me to diy Kreisel tanks, which are used to create circular flow for the aquaculturing of pelagic Jellyfish. I quickly realized that the system seemed amenable to modification to provide a high degree of linear flow in a system with very high amounts of total flow. This is something which the currently popular manifold systems don't do very well, for one main reason: turbulence. Simply put, flowing water from the narrow nozzles of typical powerheads across a distance and requiring it to enter small intakes to return to the pumps inherently creates large amounts of turbulence which detracts from total velocity. And to make matters worse, the act of all that moving water suddenly hitting a solid glass wall certainly doesn't help in regards to turbulence! But a recent thread here has shown a way to avoid having things rapidly moving across the tank from encountering a solid wall. I've thought about all this, and mused a bit with friends and online, and then a 40 gal long aquarium fell into my lap. It's 48" x 12" footprint seem a reasonably good dimension for a small scale model of my design before I start messing with the 96" x 18" 180 that is where ultimately intend to apply it. Essentially there will be an "L" shaped plenum installed in the tank. The vertical end will extend above the running water level of the system, and will be placed as close as possible to one end of the aquarium while still allowing space for the pumps which will provide the water movement. The horizontal element will extend to within approx. 4" of the opposite side of the tank to allow unrestricted return flow back to the pumps. This opening will be screened off with gutter guard as a precaution against fish entering the plenum, and a small vertical lip to assist in keeping the substrate in place will be added. The plenum will be supported on lengths of 1.5" pvc. Near the screened off end of the plenum I will be installing a double thickness of the sheet biofilters commonly used in ponds. Essentially it's a tangled woven mess of fairly large diameter polypropylene "thread" similar to heavy fishing line but much stiffer. It holds its shape well under high flow and collects and holds a lot of sludge. I believe it will also soften the transition of the water into the plenum by creating a more gradual deceleration of the water. Anyway it's my project for tomorrow, most of the materials are already on hand. Pics to follow
