Need a little help with this project

Hi guys, I have been searching for a while now and have not had these questions answered. I have been in this hobby for a few years now but just recently decided to attack the DIY aspect of it. I currently have a 150 gallon tank filled with several fairly large cichlids, rays, and an Arrowana. So needless to say there is alot of poop produced.

I am going to make a PVC overflow and these are the numbers that popped up when I used the calculator.

GPH 1700 Linear Overflow Length: 26.84 inches
Drain Pipe Diameter: 1.7 inches
Each Dual Drain Pipe Diameter: 1.2 inches
Each Dual Linear Overflow Length: 13.42 inches

I have a pump that pumps 1700GPH, The part that confuses my is Why the drain pipe diameter is bigger then the dual drain pipe diameter? Is the Drain pipe if I am just using one overflow, and the dual if I am using 2 one on either end of the tank?

Also if the linear overflow is 26.84 inches, is that the total length of the entire PVC system? or is it only the measurement of the section that is inside the tank (The U section)? I know I am supposed to find the sum of all the sides but that would make the tank around 5 inches tall? (I am sure I am not doing that correctly)

One final question is how would I measure if I am getting the full supply going to the Sump? Is there a formula I can use to decipher if my pump is working harder then the tank is draining? Rather then waiting to see which one stops working first?

 

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