If I were to want half of the tank to be high current and the rest pretty slow, what gph would be required?
. . . It's more about the design of flow than about gph. If you give the water a circular path to move in, it'll move faster given the same 'push' than if you were trying to push it into a flat wall. Water is incompressible, so without somewhere to travel to, it's not moving. The same is true with electricity. You can touch a huge charge and it doesn't really matter, unless you're also touching something else that the electricity can flow to through you. That's when it's dangerous. Anyway, my point is, if you design a circuitous path for your water to flow in, you can choose which part is fast and which slow, and you can make the faster part faster while requiring less force.
Water flow designs:
. . . 1. Circular near glass, on outside of tank:
http://www.aquariuml...less-tank-2.jpg . . . 2. From one end of the tank to another, then through PVC tubes:
http://www.loaches.c...manifold_02.JPG. . . The first design might be better than the second because flow through PVC tubes is reduced by friction against the walls. Choose a bigger diameter pipe so that the boundary effects aren't as big a deal.
. . . *nods* That's really the best way to look at it. If you just stuck a powerhead in the tank and didn't care about flow, you might end up with two regions; one highly turbulent region, and one very calm one. If you choose the path for the water to flow through then you can choose where there is unidirectional current and where the water is stagnant. In the first design, the no-flow region is in the middle of the tank. In the second design, the no-flow region is at the surface of the water and anywhere not on the straight line axis from powerhead to foam sponge. You could arrange the second design in the front or back half of the tank and leave the rest of the tank with little or no flow.
Edited by EricaWieser, 15 October 2011 - 07:16 PM.