The problem with comparing the flow in a tank to the flow in a river/ stream, is that flow in a stream is measured in ft/ sec, and not GPH.
Since one cubic foot of water is 7.48 gallons, and the MP10 (that I ordered a couple of hours ago btw) will be on one side of the tank, flowing the length of the tank, to find ft/ sec that 1600 GPH is, you need to determine how "long" one gallon of water is in the tank.
The tank is 17.5x17.5x24"
One cubic foot is 1728 cubic inches. Divide that by the width and height of the tank (17.5x17.5= 306.25 square inches) to get the dimensions of 7.48 gallons in the tank, and you get 17.5x17.5x5.64 inches. Divide that by 7.48, and you get that one gallon of water is 17.5x17.5x0.754 inches. Now you know that if you move one gallon of water/ hour, the water in the tank is moving at .754 inches/ hour. 1600 GPH is 0.754x1600= 1207 inches/ hour (in a tank with these dimensions). To get that into ft/ sec, divide it by 3600 seconds/hour, then divide it by 12 inches/foot, and you get 0.0279 ft/ second? (anyone wanna check my math?)
That isn't too much flow, but it is coming from a small(ish) point. vortechs do have very wide flow, but I wouldn't be using the full 17.5x17.5", considering the water does have to come back to the pump... however, if I have it on pulse mode, the flow would be closer to the 0.0279 ft/ second, or 1/3 inches per second that I calculated above. One inch of water flow every three seconds doesn't seem like much, but I guess I'll have to wait until I get the powerhead to see.