Coast to coast overflow design question.

[Randys]

I'm in the preliminary stages of planning/designing my next tank. I plan on an 8' tank (240 or larger), an external coast-to-coast overflow, and BA drains. I want to target the ability to run at least 10x turnover. My question is how do you determine the vertical location and height of the weir opening in the back panel of the DT?
Here's my first rough sketch of what I'm thinking. I'm guessing the overflow would be 5" from front to back, 8" tall, and 7' wide. I left 6" on both sides to make room for (2) return lines.
I drew up an acrylic tank but haven't made a decision on acrylic or glass.
Any comments, input, or directions would be most welcome.
Thanks!

 

[pacu mom]

The opening needs to be as high up as you can get it. Remember that the bottom of the opening is going to the highest water level in the tank, so if the opening is lower, the tank will look like it is not completely full.

Here's the back side of one of my overflow boxes.

Here's a view from inside the tank. You can see where the water level will be.

 

[Randys]

Thanks for the pics!

But isn't the water level in the tank determined by the pump output vs the physical size of the weir opening? I have a trapezoid overflow in my 90 gallon and am pushing enough water to where the water level in the tank is at least 1/2" above the bottom of the openings (teeth).

And wow, that's a big tank.

 

[pacu mom]

Thanks for the pics!
But isn't the water level in the tank determined by the pump output vs the physical size of the weir opening? I have a trapezoid overflow in my 90 gallon and am pushing enough water to where the water level in the tank is at least 1/2" above the bottom of the openings (teeth).

That has not been my experience. The only time it is slightly higher is when filling the tank and the return pump is off, or there is a clog in the prefilter in the overflow box. I suppose it is possible to have the return flow faster than the flow from the overflow box.

 

[Randys]

Yes, the more water you pump into the tank the higher the water level will be. Carried to the extreme the water would overflow the tank.
I was just wondering if there's a rule of thumb on the location and depth on the opening while realizing this is dependent upon the area of the weir opening and the pump output.

What size IS that tank??? It looks huge!

 

[pacu mom]

15' x 4' x 4' Hopefully after 5 years, we will have it up and running in the next couple of months. Plan on returning the water from a 405 gallon sump with redundant filtration to the main tank via a Barracuda Gold pump/ Ultima II 4000/120W UV sterilizer. Will have two closed loop systems drawing and returning water directly to the main tank for mechanical filtration and additional biological filtration.

Do not anticipate the water level to be higher than the bottom of the overflow slots...even with two Barracuda Gold pumps and one Hammerhead pump returning water to the main tank. Would love to have the water level a little higher, but it's not going to happen.

 

[DN328]

That tank is going to look nice, Pacu.

OP, I had the opposite dilemma where I wanted my water level lower, so I had to make a jig and drill additional drain holes on my internal overflow.

You should first decide where you want your water level to be. I find that the water level won't be much higher than below the weir holes/teeth.