Tank Design Help

[sphelps]

Originally Posted by Canadian

because sphelps is contending that a larger overflow would decrease the suction of the overflow and make it less efficient.

Not necessarily, I'm saying the size of the overflow is more dependent on the flow rate than anything else and that bigger isn't always better. Practical experience and results, including your own example, shows overflows work better when properly sized and if the overflow is too large for the flow rate you may end up with surface scum build up.

With a longer rectangular tank i think you're better off with a single overflow on one side and return on the opposite. This way you're pushing the general flow towards the overflow and not away from it and filtered water has to travel the full length of the tank before it can be skimmed off again. It just makes more sense to me.

[Canadian]

No, in my example I would contend that while 3" is adequately sized to accommodate the flow rate, even at 4" the majority of the water flowing over the overflow is coming from beneath the water's surface and I would benefit from an even longer overflow to improve the efficiency of protein-laden water being drawn off the surface.