Help w/ external overflow

[supermarvin76]

I would like to design an external overflow, but would like some input so I can do it correctly the first time.

Using the over flow calculator on here, I noticed that for 700 gph (if I remember correctly) I need 13 linear inches. However, I was thinking on a 30" wide tank, I would like to have an external overflow of 20-24". I will be using a pump with approx. 500 gph return after head loss.

Do I need to worry about having "too much" overflow?

Once I settle on the width of the overflow, does it matter how deep I make it? If so, how do I determine that?

This is really the only way I want my overflow, but my last thought is that I am very hesitant to go this route because it just doesn't make sense to me how silicone actually holds all the weight and glass together of the overflow box.

I would appreciate all info, and tips, or links.

Thank you!

[needmore-reef]

Look at CPR’s design, Marine depot has detailed info on each model. Good luck I tried making one and there are a lot of details and all seems must be perfect. I couldn’t get mine leak free. Also make two in case you loose siphon in one. I have a tank with two, each able to handle the flow of the return pump. I have come home several times in the last 3 years and found one overflow box not working.

[fishoutawater]

I have made two, one on a 29, and another on a 40 breeder. The breeder overflow is 26" long, and the return pump is sending around 450-500gph over it. The overflow dimensions are 8 x 4 x 26. My next one will be one inch wider to make service in it easier. I love the external, makes your tank sooo much easier to work in, scape, etc. Also much safer, I have had a couple anemones wander around and end up blocking part of the overflow. With a typical overflow I may have flooded, with this one it was not an issue. Water going over is only about 3/16" inch. I plumbed it with a 3 drain system(BeanAnimal setup)
http://i288.photobucket.com/albums/ll191/fishoutawater/100_3943.jpg
http://i288.photobucket.com/albums/ll191/fishoutawater/100_4177.jpg

[supermarvin76]

The second one is the kind I am looking for information on and assurances about their longevity.

What is the "BeanAnimal setup"?

[Harry_Y]

Look at the Glass holes overflows they are internal but quite small

[BeanAnimal]

The overflow calculator on the RC homepage is somewhat confusing. It indicates the minimum linear overflow length needed to achieve what is considered adequate surface skimming. In most cases, it is desirable to maximize the length of the overflow weir to maximize the surface skimming effect. Within reason, you can not have too much linear overflow length.

There are several ways to construct an external overflow. If your tank is glass, then you should use a glass to construct the overflow and it should be adhered with industrial grade silicone adhesive. If your tank is acrylic, then the overflow should be acrylic and bonded with solvent.

I will assume your tank is glass. The silicone will create a strong enough bond to secure the overflow to the back of the tank. You can either cut down part of the back wall (with a continuous rim diamond blade in a grinder or circular saw) or you can install a very narrow internal overflow that route water to the external box via several holes drilled with a diamond hole saw.

Getting water to the sump is a different story altogether. You need to select a standpipe topology that meets your needs. However, first lets get the actual overflow boxes worked out and then we can size them to fit your standpipe (drain) option.

[fishoutawater]

The second one is the kind I am looking for information on and assurances about their longevity.

What is the "BeanAnimal setup"?

Not sure I understand, they are both external boxes on different tanks, built and plumbed exactly the same way. As Bean commented, you have to use like materials, glass w glass, acrylic w acrylic. Shouldn't be hard to find the "Silent and failsafe overflow" thread, don't need to read the whole thing, the concept is well written and covered in the first several pages of the giant thread. It should last the life of the tank. It will run silently, and is much safer to run than a conventional single drain overflow system. I have never heard of anyone running one and not loving it. I will never have a tank without one again and am currently in the process of building another one right now. I have been using the one I have now for almost 3 years. If you do it, spend the extra few bucks and use a gate valve and not a ball valve on the primary drain.

[supermarvin76]

Not sure I understand, they are both external boxes on different tanks, built and plumbed exactly the same way.

Sorry, I meant that I was looking for something like what you had posted, and not the first poster.

The tank this will be going on is 30x18x18. Does anyone have recommendations for the width of the cut in the tank for the external overflow, or the actual dimensions of the box itself?

There is a glass shop in town here. should I just order the glass for the box from them, and have them cut it to size?

Thanks!

[supermarvin76]

If I went with the glass holes over flow, would it be possible to plumb the tank to use two of the 700 gph overflows?