I am planning on building a HOB overflow for my tank. The only problem I am having now is making sure I have calculated the GPH correctly. Basically The way I drew it up(I don't want to take credit for the design, I copied it from another forum) it has a "chamber" that measures 3 3/4 inches x 1/2 inch instead of a "U tube". If I am correct the chamber is the equivalent to a 1 1/2 inch diameter pipe. I calculated the inlet of the chamber to be 1.875 inches. I used another calculator to convert the area of the square to the area of a circle which came to be 1.545 inch diameter, or a 1 1/2 inch pipe. Is this correct?

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75 Gallon Planted

Your math adds up. The area of your 'chamber' is 1.875 inches squared. The area of a circle is PiR^2. This comes out to a radius of .7725 inches. Or a 1.545 diameter.

I was hoping I did that right. It has been 20 years since I took a math class. Now the only question is if my overflow is going to be able to handle 650 GPH. I never thought I would be doing this kind of math for "fun".

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75 Gallon Planted

I'd imagine you will be fine unless you are taking a round about trip to the 4th floor and back or something crazy. Good luck with your project.

I don't know what I was thinking when I posted that I wasn't sure if the overflow would be able to handle the 650 GPH I am gonna push through it. The way I have it set up it will be the rough equivalent of a 3 inch pipe. When I get done fabricating this thing I will post pics and what not (if I ever can get started on it).

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75 Gallon Planted

diameter of pipe = how many gallons pipe can handle per hour
.5" = 90 GPH
.75" = 220 GPH
1.0" = 375 GPH
1.25" = 580 GPH
1.5" = 840GPH
2.0" = 1500GPH

So your well within your range

Yeah, I would say I am going to be fine. If a 1" pipe can handle 375 GPH I can cut the overflow in half the way I currently have is drawn up. As it stands i think the Max GPH that it can handle is probably 1800+ GPH which is far beyond what would ever be pushed through it.

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75 Gallon Planted

Okay, I am extremely frustrated at this point. I have built my overflow, well half of it, and it cant even handle a gallon of water dumped from a milk container directly into the pipe through a funnel. The siphon u-tube keeps getting air in it when water is moving through the overflow but not when there is no flow. I have tried to test it in a bucket that is being fed by the bathtub faucet and it can kind of keep up but still has trouble. What am I doing wrong?

Here is a picture of what I have so far.

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75 Gallon Planted

This place will fix your problem: CPR AQUATIC, INC - CS Overflows

Actually that place will give me more problems being as I don't have or would I spend $120 on an overflow box.

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75 Gallon Planted

Just trying to help out.....

They were the ones I used to use.

I wasn't trying to be rude, but there is a reason why I am making an overflow opposed to buying one. It cost me about $20 after everything is said and done to make it.

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75 Gallon Planted

I went with this design. Works Great!
Dramatic AquaScapes - DIY PVC Overflow - Page 1