Fitting a weir/overflow

[carpboyjoe]

I have a large tank that was built a few years ago. Long story short it should have had a weir at each end to cover stand pipes,but it does not.
The main reason for this is in the event of a bulkhead leak it would be an entire drain down.
The tank is 28" tall and made from 1/2" glass, my question is do I need to use 1/2" glass to build bottom to top overflow or can I use thinner glass to build it.
Thanks

 

[duanes]

Weirs can be partial or fit entirely to the bottom (there are no rules), or you can build a simple one from PVC that rests atop the stand pipe, or just be a tilted piece of PVC atop the stand pipe.
[/URL[URL=http://s70.photobucket.com/user/dstuer/media/overflows/IMG_0742_zps95b48373.jpg.html]
I sometimes ad a Tee with an extra slot for redundancy in case 1 is plugged

Below is a standpipe with a strainer cap screwed on functioning as a weir
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[DN328]

I've not done it, but I don't believe you need 1/2" glass for the weir. Do you plan to have teeth in the weirs?

FWIW, I have a 28" tall 1/2" glass". I had an internal overflow built and they used black acrylic - they use that on all overflow. It hides the pipes as well. Zoom in and look towards the left end of the tank and you'll see the overflow box for visual.

 

[ragin_cajun]

You can use acrylic for overflows. It's sumps that you want to use glass for a glass sump and acrylic for an acrylic sump. The reason is the materials should be the same so they expand and contract the same. If glass sump has acrylic baffles, the tank could contract a little from temp fluctuations, the acrylic baffles contract a little less, and now there's outward stress on the walls of the sump...which could crack the walls of the sump.

Inside a tank, the overflow is not glued from one wall to another, so this is not a concern.

So, go with a black acrylic overflow box for your tank.

All that said, I've never installed one, or bought one, so I don't know where to go next.

 

[DN328]

In my case, the acrylic is inserted for essentially the height of the tank and (black) silicone on both sides. The reason being is, you don't want water leaking out from the overflow box side back into the tank. The idea is to keep the water level stable on the overflow side for your Herbie, BA, etc..

I'd go measure and get some 1/2" acrylic at a place like your local TAPS Plastics or equivalent. They may be even cut the teethe for you for a little extra (although I've never asked myself, it's worth a try if you don't want to router it yourself). One key design consideration is an internal overflow does play a part determining your tank water level. So you want to make sure the teeth are cut low enough to accommodate for the water level you want, AND, still provide surface skimming. You can turn the return pump to max if done right, but lowering the water is a challenge IF weir/teeth cannot handle the return flow.

Some folks (primary reefers) avoid the teethe all together and just have a straight edge across the weir. Of course there are then considerations like small fish and bigger things that can slow down your drain pipes.