Tank Design Help

[Canadian]

It doesn't increase the velocity of water flowing over the overflow, it increases the velocity at which surface-bound proteins are removed because only the surface water travels over the overflow instead of half of the flowing water coming from below the surface.

There's a rather succinct example in the link I provided:

Surface Renewal

An extreme example: Take two identical 40' wide ponds that are fed with the same amount of water, one with a 4' wide dam and the other with a 40' wide dam. It follows that for the same flow (lets say 100 gallons per minute) over the dam, that the narrow dam will have a very thick waterfall and the wide dam a very thin sheet of water cascading over it. Now place an oil slick over both ponds! It will take significantly longer for the 4' wide dam to clear the slick fro the pond. Why? Because much of the water flowing over the dam is from below the surface! Now apply this logic to your tank, but instead of an oil slick, understand that the surface of the water attracts organics from the tank. The logical conclusion? For any given flow rate, the wider the overflow, the better your skimmer and/or in sump filtration will work!

[sphelps]

Originally Posted by Canadian

It doesn't increase the velocity of water flowing over the overflow, it increases the velocity at which surface-bound proteins are removed because only the surface water travels over the overflow instead of half of the flowing water coming from below the surface.

There's a rather succinct example in the link I provided:

Yeap I know what you're getting at but again like I said before theirs obviously a limit to how small the overflow can be. If you compare a 40' overflow to a 4' overflow of course the 40' will work better since water level will be significantly higher above the overflow. What I'm saying is a 20' could clear the oil faster than a 40' depending on flow rate.

Your theory is sound but I don't think the biggest overflow is necessarily the best. If the overflow is too big for the water flow insufficient surface tension could result. I've seen this before. The way I see it is the second overflow is not needed so why waist the space?