Ok, so I'm building an overflow box, and before having one, I think they're great. I understand that as long as your return pump doesn't exceed your overflow box rate in GPH then your ok. The other thing I see from built boxes is that they will not continue to drain water once the return pump is turned off (another great thing). The only thing I dont understand is how the siphon is continued once the power is turned back on.

Are there any specific dimensions I must know of in the construction and placement of the siphon tube or the relation to water level in the tank for this to work properly?

As long as both ends of your U tube are below water then it will continue its siphon once the electricity is back on.

There are some benefits with some designs over other designs. For instance compare these two:

Lifereef Filter Systems (http://www.lifereef.com/frame.html)
Economy Prefilter Boxes, 6 gpm (http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/4982)

If I had to pick from the two above I'd definitely go for the 'Life Reef' overflow. Primarily because the outer compartment is quite longer than most other siphon overflows. When it comes to creating a strong and fast siphon … the farther the drop … a stronger/faster siphon will be the result. This is why the Life Reef models are rated for higher volume even though they are of similar dimensions to lower gph rated overflows.

Also you'll notice that the Life Reef overflows have a baffle in their outer compartments and their stand pipe is set low. This baffle keeps the U tube below water at all times (even during power outages) and since the standpipe is set lower than the baffle it ensures top performance with its siphon action. With some study of the design you’ll see what I’m talking about.

Before actually making one yourself you might consider purchasing one. My 1st overflow was the Equatic Eco one and I’m VERY glad that I didn’t fiddle with making one myself.

Also the very best type of overflow is an internal overflow (not a siphon). Even 1 corner overflow is much more reliable than any siphon overflow. For the price of a couple pieces of glass, a cheap diamond hole saw, and a tube of silicone … you could have one of the best overflows possible and at a lower cost.

I will have to agree with RandyStacy. I wouldn't DIY an external overflow myself-- just too much risk. For about $30, you can get a more reliable design than a DIY. (I shouldn't say "reliable" since external overflows are known to be unreliable..lol)

If you have to have an external overflow, go with the one where you can put an Aqualifter pump to suck the air gap in the U-Tube. It adds more "reliability"...

xtmreef,

The only problem with overflows that use an Aqualifter pump (CPR Overflows) is that their overflows WILL FAIL without them. They are not an option ... they are a requirement.

CPR overflows do not use a simple U-tube, they have a HUGE weir. A weir I suppose is similar to a U-tube, but it's just enormous in comparison. Since it's so big, the speed of the water flowing through them is extremely slow in comparison and this encourages air to be trapped inside the weir. This air will accumulate and eventually break the siphon. This is why an Aqualifter pump is a requirement.


SoCalReefer,
The Lifereef overflows are extremely reliable and worth every penny. People who have had their overflows fail in the past would agree :) The 'economy overflow' that I listed works fine too, but it was not complete in my opinion. I installed a Durso standpipe (http://www.dursostandpipes.com/)inside of mine and that made it absolutely dead silent. Without the Durso it made slurping sounds that were unbearable. Other than that it has been rather reliable.

I'm just extremely happy to be rid of siphon overflows for good. Whenever I go out of town I'm concerned about the siphon and I always have to make sure that the U-tube is clean. Just know that with a siphon you are relying on a piece of equipment to transfer water to the sump rather than simple gravity (with a drilled tank). $hit happens.

I have a CPR overflow, and I use an Aqualifter pump as stated ealier, but I can tell you that when, not if, your aqualifter pump fails, you will wish you had a built in overflow. I was a family vacation for 11 days when my housesitter called to tell me my fish did not look "happy", without going into the details, an $11.00 pump cost me a whole bunch of money, a lot of stress, and I just might have offended Mickey Mouse (and the rest of the fine staff at Disney) when I was told by phone that the soonest I could have a new aqualifter on my doorstep was 72 hours. I now keep two extra on hand, but have a new tank on order and will use my aqualifter for a paperweight.

Okay KG, now you have to start a tank journal and not keep us in suspense!

Randy some great advice. I've been gleaning over your webpage for DAYS and getting a lot of great info from it. I have to say the DIY bug has got me, mostly since most simple designs for equipment and "economy" products are still expensive. I'd much rather keep money in my pocket for livestock and the cool stuff.

Quick question for you. Are you using the Durso standpipe, DIY Stockman Aquasilencer or Hofer? I think the Hofer looks pretty simple to make and should fit best in my DIY overflow box I plan on making. I figure my back compartment to be around 6" long, 5" wide and about 10" deep to get a good amount of space to tune the standpipe and create good siphon.

With that said, I am setting up a 75g FOWLR glass tank, DIY stand and hood, 18gal (converted glass tank) sump, 216W of T5 lighting, with a Rio 2100 pump for return. Since I have a non-drilled glass tank my fiance bought me last Christmas, I'm going with an external overflow and won't risk a break drilling the side and be SOL with a bunch of equipment.

I'm going with a DIY overflow as well as a DIY 5" recirc skimmer mocked off of your designs and a Deltec AP600. I went to a local TAP Plastic and got about 20lbs of scrap Acrylic for 50 cents a pound, and some 5" and 3" acrylic tubing. I am pretty handy so I'm sure my end results will be functional but maybe not extremely pretty!

I plan on putting some of this down in a tank build log here as soon as I can clear out some space to finish my stand :)

Thanks!

Brian

OK Randystacye, or anyone who can help me with BABY STEPS in this! I do not yet understand this part of my tank yet, but need to begin learning because I am getting ready to begin with corals (have very few 'starters;colts, star polys, xenia, tube corals). My next mission was to figure out just how much flow I have. My flow is much better when that overflow is slurping like crazyIt drives us all crazy.
siphon? I have a 55gl pre-drilled/overflow. Can you, or anyone tell me what I need to do to cut down on the noise without cutting down my flow?

do you have a stand pipe connected to the overflow drain ??

I am going to guess thats the waffle-hole plastic pipe that I have a sponge filter slid down over
BEAR WITH ME!

nope ... this is a step by step instruction article, that Renee was great enough to grace us with, on how to build a stand pipe (that should stop the gurgle ...

http://www.talkingreef.com/forums/diy-projects/2890-build-your-own-standpipe.html

i remember that thread, SHD did a great job explaining it.

I somewhat differ in option over the glueing part- making a completely sealed unit, & the venting hose. Venting hoses are solutions of the past (no offence SHD - you old school trojant;)) To give an example guys- When i was building my nano (only cause its fresh in the mind & not beer4gotten) out of that new age funky irragation materials, because its made to be completely sealed, there was no choice but to find an air control piece.

But as soon as your using PVC, the rules change - I prefer to whistle cradle my top cap & leave the stand pipe only assembled by hand. Think of the standpipe as a living breathing entity , the more restricted you make it, the more that can potentially go wrong. Plus it can potentially balance osmotic pressures far better from multiple sources rather than starving or fighting for it at our pre determined locations. Does this make any sence?