Overflow box water level
 

Where should the water level in an overflow box be? Can we even control that? I am building a no teeth box and figured on putting it just above the trim level so the water surface is not visible. Where would the water level in the box be: at the bottom of the hole, halfway full or would it be above the fitting? For a herbie design what should the height difference be between the top of the back up drain and the bottom of the siphon? I am trying to figure out if the holes should be on the same line or staggered a bit.
I am using 1 inch bulkheads, flexible tubing, and the box will be roughly 7x4x5.

You should adjust you running levels in the upper containers and your sump to prevent floods.

On power out the water that drains to the sump should not flood. So you have to adjust the running water level low enough prevent the flood.

In the case of drain blockage you need to adjust both you upper container(s) levels and the sump levels so that the sump runs dry before the upper containers flood.

Not much help but basically you do have to adjust untill things work.

The lower you keep the upper container level, the more water can be pumped from the sump with a drain failure before floods. And the higher the sump water level can be. So there is a tie in between the two. I usually set the upper container at some astetic level say right at the bottom of the top trim line. Then adjust the sump level to prevent floods.

my .02

Will this have an auto-restart if the power goes out?

Yes.
That is another thing you check for.

But even with an hob overflow that breaks siphon, you should adjust so that even in that case you don't get a flood. Again, the sump runs out of water before the upper container floods. I test for that by just forcing the siphon break/ drain blackage.

I also use the return pump or a powerhead to suck out any air in a hob design. To help prevent siphon breaks and reestablish siphon should siphon be lost.

I also make overflows from pvc pipes with a water trap design. So the overflow boxes are not necessary. But then ugly pipes are. :lol:

my .02

I never cared for siphoning water out of the tank. I used a CS90 for a long time with no problems (in fact it started right back up after a few power outages, no problem) but I always think about it while I am at work or away.

If anything, I prefer to drill at least the back of tank (coast to coast overflow) or buy a reef ready drilled bottom. Glassholes.com has a good kit for putting an overflow on a tank. If not, you can probably DIY the process with a Diamond hole saw and a bulkhead.

I plan on drilling the tank so auto restart shouldn't be an problem unless the return pump wont start, but that wont make a flood. I am more concerned about the herbie getting blocked. There can be a pretty significant difference between the siphon plumbing and the top of the back up overflow. I don't want the water level raising 1.5 inches before it reaches the top of the back up elbow.

Thats why you use 3 lines, and not 2. 2 are for intake, the other is the failsafe. You can also shave down the pvc so that it won't raise that high, if thats a concern of yours.

I considered that, the Bean animal overflow, I am waiting for the Reefingmadness overflow that uses 4 lines. Haha. Does anyone know if the water just comes up the elbow, flows over with minimal depth and down to the sump or does it fill the horizontal halfway or all the way? Or am I making an issue out of nothing. Maybe I should just build it and let it fly.

Reefing Madness Overflow- To be continued. =)...j/k I use a CPR Overflow box with Aqualifter. I don't have any problems, and I turn it off twice a week for Mysis feedings.
Anyways, the pipes will take the water down, it won't fill the box with water per say. But, here look at this, it will give you a good idea what your looking for as far as water and what nots.
Bean Animal's Or Herbie Over Flow (Version 2) - YouTube

"I am measuring the rise with the help of my finger"- best line in the video. Thanks for the laugh. It took me a few minutes to realize what a "gas kit " is but it was a helpful video.

I am typing this reply with the help of my fingers.