I just finished testing my DIY overflow box. Other than a minor plumbing issue
with the drain connection out of the bottom of the box my big concern is flow capacity. I have never kept Salt Water fish and have been doing research for months, and slowly working my way into this.
Every thing I have read says I should have 10 times the circulation as I do capacity of water. So if I have 100 gallons capacity, I need 1000 gallons circulating capacity. To get 1000 gallons per hour moving through a pipe, that pipe would need to be about 1 inches in diameter under about 40 psi. That is a rough estimate based on my own situation of my water supply of 3/4 inch pipe at 40 psi giving me 650 gallons per hour. I have watched video of other peoples sump setups on you tube and I am not seeing this volume of water movement.
My DIY box gives me about 150 gallons per minute out the bottom. That is with two 3/4 dia siphon tubes draining into a 1 inch drain tube to the sump. At this rate I would need 6 boxes lined up across the back of my aquarium to keep up with a pump. What am I missing?

You don't need to turn over that water in the sump. And 10x the turn rate is FOWLR, at minimum. A 1" gravity fed pvc will run 600gph, your restricting it by running the 2 lines into 1, don't. You just need powerheads in the tank and at least 1.5lbs of Live Rock in there, the powerheads turn the water over for you. That is all the is needed, the sump is a bonus water scrubber for you.

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+1 and just to add you wouldn't want that much water running through your sump that fast. Add a ball valve on your return line to balance out your overflow versus your return. A pump like a mag 7 or 9 would be enough to turn over your tank enough times.

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Only question now is how do I get 600 gallons per hour through a 1 inch siphon tube. I was only getting 150 per hour with two siphon tubes and the one inch drain to the sump was not running full by a long shot.

1.5 pounds live rock. I assume your mean 1.5 pounds live rock per gallon? That is 112 pounds rock, at $10 per pound average. $1120 worth of live rock?

That's where the ball valve comes into play. The overflow is only going to allow so much water into the sump. You have to make sure you are not putting water back into the tank faster then the water is flowing back to the sump. The way you do that is slow the return down. This is where this hobby get fun. While you are doing this balancing act you have to sit there to make sure you don't flood the sump or tank. Even with a 1 inch drain and a overflow running 600 gph using a pump that is atleast 700gph you will be able to keep up the water cycle. And also keep this in mind. Make sure you have enough room in your sump just in case you loose power it won't flood your sump. I use a check valve on my return line so not to cause a back siphon. Add a picture if you can so we can see how you have it laid out.

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Check craigslist to see if you can get a better deal on live rock.

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I understand the ball valve operation. I still do not understand how to get the overflow tank siphon tube to transport enough water over the rim of the tank. Today I am going to test a 1 1/4 siphon tube. It is flexible vacuum line tubing for a swimming pool so I can keep it from going flat at the bend, but I see no purpose in buying a 600-700 gallon per hour pump then cutting it back to 200 gallons per hour when I can buy one that delivers that to begin with and save money. I'll post a picture of the test setup when I can later today.

My only experience with Craigs list up to this point was buying a tank that was so dirty I broke it trying to clean it. I can't drive so I have to buy stuff I can have delivered.

Just get a couple of lbs of Live Rock and the rest Lace Rock. I've only got 40lbs of LR in a 240g, but 280lbs of Lace Rock for the rest.

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You would think by just matching the numbers it would work. The thing you can't count on is travel time from the tank to the sump and back to the tank. This is why in the past I've used a pump that was rated alittle higher then the overflow. Right now I have a mag 12 on a 90gal. tank with a 30gal. sump. my drain is 1 1/4 inch with a 1 inch return. And the pump is wide open. If you are running a skimmer in your sump you have to count for that water as well.

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That's understandable. I also agree with the post above using lase rock to make up some of your poundage.

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I live in Texas so Texas Holey Rock isn't so expensive where I live. Is that the same as Lace Rock. I have heard the terms used together.

I can get plenty of water from the bottom of the overflow box into the sump. Keep in mind that this is a hang-on-the-tank overflow box. I can't get enough water over the rim of the tank through the siphon tube. My guess is there is not enough drop in the siphon tube. So I am glad I didn't buy the commercial model of the same design.
Time to design a new one. Before anyone tells me I should, drilling the tank is out of the question. I have already broken one tank, I am not going to break this one. This one is new.

I am always leery of DIY overflows, too much is at stake and too much can go wrong with catastrophic results.
My present system has an internal overflow with a single 1" standpipe ad I easily get 700-800 GPH through it, enough that I can run an OceanRunner 3500 return pump full blast with no restricting with the installed ball valve.

I would look at something like an EShopps overflow box. They are very reliable, I used to own a 1000 GPH version that used two siphon tubes and two drains and was very inexpensive. I think I sold it used for $35. Look on craigslist or ebay, I'll bet you can find lots of them.

I am all for DIY and have built my sump, lighting, stand and canopy with cooling fans and much more but an overflow is not one I would feel comfortable sleeping at night with.

Being in the manufacturing business myself, I have discovered that the difference between DIY and store bought is research, tools, and talent. Just because you buy it from someone else, does not mean it is better. The aquarium stand in my photo gallery would sell for over $1000. It cost me less than $20. But then I have $15000 worth of woodworking tools at my disposal

Could not agree more.
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When I was younger my Dad asked me a question " what's the difference between a good mechanic and a bad one" ? the tools he has or don't have. I've seen some good DIY overflow and I've seen some disasters. I would use one I made(I don't trust myself that much) but with all of them somebody had to make it. In the past before I used drilled tanks I used those u-tube overflows and never had a problem.

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I am the same and DIY anything I feel comfortable with. My oak stand and canopy are one example.


The sump is another:


The ATO is yet another:



The original lighting is another:


As is the current LED mounting arrangement that gives me the ability to move the fixtures anywhere over the tank in all directions:



But even though I am a water/wastewater system operator and maintenance person by trade an overflow is not in my DIY picture. You will never get glued or screwed PVC fittings to flow as well as mandrel bent U tubes on a hang on back. I did DIY the modified Stockman standpipe in my internal overflow box though and it works great. No bends of changes of direction to worry about.

Sorry If I sounded critical. I didn't mean it that way. And, on considering your statements, I have decided to go with the HOB style. The manager of the pet store where I shop has one he never used and will sell it to me at a discount.
I just don't want a bunch of pvc pipe in my tank spoiling the look.

I love your Stand and canopy. Beautiful craftsmanship. My stand is in my photo gallery, as well as a picture of the beginning of my sump. I did not build a canopy because the only place in my house that it can sit is under a window in my living room. (North side of house under a deck. No direct sunlight.) Blocks about a third of the window as it is.