Type of internal overflow box?

[freshera07]

Is it better to have those from top edge to bottom edge internal overflow boxes or the short ones?

[heyfredyourhat]

.....Do you mean a vertical overflow box vs. horizontal?? I say horizontal, or coast to coast. It will give you the most area to surface skim...

not sure if thats what u are talking about tho

[freshera07]

I'm talking about like those mega overflow black boxes at the corner from AGA that cover the entire corner from top edge to bottom. Or if I should install like a small box with teeth as a skimmer like those that come with Utube overflow sets. Those small box only cover from top edge to like the middle of the back glass.

Hope that cleared it out

[Travis L. Stevens]

It doesn't matter much if the overflow box reaches all the way to the bottom or not as it really isn't taking much water, if any, from the middle or bottome of the aquarium. What is the key is the amount of surface area that is skimmed off the top of the water per pass. In order to do this, the larger the parameter of the overflow box's footprint the better the skimming.

For example, let's say you have two rectangular overflow boxes that will attach to the back of the glass like so...

___Back of Tank__
|______|

^ Overflow box

You have one that comes out from the glass 2" and is 8" wide. You have another one that comes out 4" and is 6" wide. Both boxes have the same width of wiers between the teeth and the same width of teeth. The usable parameter for the first box is 2+2+8=12", and the usable paramter for the second box is 4+4+6=14". Knowing that the weir size is the same, you'll get more usable skimming capacity out of the second one. A large factor is the negative space between teeth since this directly effects the amount of water than can pass through. The "Calfo Style Overflow" (AKA Coast to Coast; AKA Horizontal Overflow) stretches from one end of the tank to the other, and has no teeth. Therefore the actual usable surface skimming is the entire length of the tank. But that might not be feesible for all tanks.

Basically, the larger the box and the wider the space between any teeth the better. Just measure all the negative space.