Glass Weir Tips- Dos and Don'ts

[rlinusc]

I am considering constructing a glass weir internal coast to coast overflow for my 72" tank. I want to make sure though that i am not missing something.

Essentially, it seems as if i would get 2 long pieces of glass (72" x 5") and 1/4 " thickness and just silcone them to the tank creating a box?

Assuming i use the right silicone and measure it correcting to allow for flow, is there anything i am missing?

I have been trying to find a good thread on this and can't quite find one.

 

[mmn]

That's what I did. Same size. Just allow an 1/8" or so on each end for the silicone.

Regards
Michael

 

[sleepydoc]

Yes. Measure twice. Check the tolerances of the glass shop. Most are pretty accurate with their cuts, so you can get by with ⅛" total gap, but ¼" would be fine.

Design your overflow, overflow plumbing and bulkhead positions before you have the glass cut. It's a lot easier to fit the glass to the overflow than the other way around.

Also, consider if you want a strictly internal overflow or a combination internal/external. The latter potentially takes up less room behind the tank, but is a bit more involved.

 

[NanoReefWanabe]

1/4" glass seems a touch light for a 6' span. ..I would be more incline to use 1/2"

 

[lawdog75]

1/4" (6mm) glass should be perfectly fine. The thickness of glass in aquaria relates to the volume of water it is containing not the length generally. An external weir of 6' x 5" x 5" will at max hold 18lbs of water or 40kg. Taking I to account the flex of the glass over the unsupported span and the hardware to allow water to transition to the sump it still should pose no issues as the bottom panel will be secured over a 6' length with the two end also secured to the tank.

If you are overly worried then a couple of 4.75" x 2" baffles to secure the external horizontal pane directly to the dt will provide peace of mind. Baffles if fitted flush to the top will still allow water to flow to the drain efficiently and with less turbulence.

Just my 2c

 

[asudavew]

1/4" has been fine in my 6 footer.

The glass is the easiest part. Pay attention to your layout for you bulkheads.

 

[sleepydoc]

1/4" glass seems a touch light for a 6' span. ..I would be more incline to use 1/2"

A 6' x 5" span of glass on its own would coause concern, but remember the bottom piece is anchored to a vertical piece on either side, and the side piece is standing on edge and anchored to the bottom. They essentially form a long corner with each one stabilizing the other.

I have ¼" glass in my 120 (4' long) and it is rock solid stable. I can't imagine that a 6' piece would be that much worse.

 

[rlinusc]

I will definitely sketch it out before I order the glass etc. thanks

 

[Jay_R]

One thing i failed to calculate when installing my weir was the additional water height when the weir comb was added to the top of the weir glass.. it's not an issue, but when the weir comb gets clogged the water level rises just enough to touch the underside of my light unit. Pull out and clean off and i'm back to normal. But should have lowered the weir by half inch just to be safe

 

[RocketEngineer]

One thing i failed to calculate when installing my weir was the additional water height when the weir comb was added to the top of the weir glass.. it's not an issue, but when the weir comb gets clogged the water level rises just enough to touch the underside of my light unit. Pull out and clean off and i'm back to normal. But should have lowered the weir by half inch just to be safe

You don't need a weir comb and in fact it cuts down on the entire point of a coast-to-coast overflow :headwalls:.

 

[svynx]

Get the edges of the glass polished. It looks cleaner, and you won't cut yourself working with or near the glass.

 

[intyme]

Get the edges of the glass polished. It looks cleaner, and you won't cut yourself working with or near the glass.

To polish the edges, just take some sand cloth( like plumbers use to clean copper) and run it back and forth and it will knock off any sharp edges

Sand cloth usually comes in a roll

 

[EvenFurther]

I've used my air powered palm DA sander to knock off the edge. I just wet sand it so I don't create glass dust particles.

A raw glass edge is crazy sharp. Be careful.

 

[Jay_R]

You don't need a weir comb and in fact it cuts down on the entire point of a coast-to-coast overflow :headwalls:.

Disagree.. the the weir comb stops fish, snails and debris entering the overflow and makes no difference to it's effectiveness. To each, their own

Although that said, I have a hawkfish that seems to manage the jump and spends some time out in the weir feasting on the amphipod population that thrives in there.

 

[mmn]

Disagree.. the the weir comb stops fish, snails and debris entering the overflow and makes no difference to it's effectiveness. ...

You can disagree, but what rocket said is still true. If you have an overflow that's 6 feet long and you have teeth the same size as the gaps, then the effective length of the overflow is 3 feet. Actually a little less due to surface tension and friction.

 

[Jay_R]

You can disagree, but what rocket said is still true. If you have an overflow that's 6 feet long and you have teeth the same size as the gaps, then the effective length of the overflow is 3 feet. Actually a little less due to surface tension and friction.

Having a weir comb doesn't stop the weir serving its fundamental purpose so suggesting it defeats the object is incorrect - it just doesn't. It also has the added bonus of preventing expensive purchases disappearing down the drain - which 'isn't' 3ft in diameter.

Here's something to consider... due to the comb, wouldn't the water velocity be higher between the teeth thus creating 'improved' skimming on the surface as the water needs to travel faster through the teeth ( Causing better movement toward the weir ) - maybe even counteracting the reduction in length?

Prepare for twisted knickers lol - All i know is, with or without a comb the surface skimming happens.

 

[RocketEngineer]

Does surface skimming still happen? Yes. Is it optimal to have teeth? Not by a long shot. And that is the point. (Oh and the 3ft comment was weir length, not diameter).

Surface skimming is a function of uninterrupted length. Lots of little interruptions allow oils/proteins to stick to the face of the teeth instead of getting pulled over the weir by the water flow.

As an example, here is a picture of my return and 1/2 my overflow:


Do you see the encrustation along the end of the overflow box? That is where water doesn't flow over the box because that piece of glass is 1/4" taller than the front edge. I get an oil slick in that corner even though it is right next to the main weir edge. If that one piece of glass had been cut the same as the other end, I wouldn't have algae buildup on that side of the box.

The same thing happens with the teeth. There is a concentration of nutrients at the surface of the water right next to the surface of the tank. Hard surface + lots of light + nutrients = algae. Therefore you are more likely to grow algae in the teeth which further reduces the surface skimming capability of the weir.

So, how do you keep things out of the box while maintaining that long clear edge? A lid on the box with a vertical lip that just barely clears the surface of the tank. Lots of folks have them and aside from the rare fish who can shoot the gap, they work amazingly well.

 

[Jay_R]

lol seems you're passionate about the use of weir combs.. as I said earlier.. To each, their own. A little wipe once every three months to remove a minuscule amount of whatever is certainly well within my capabilities.. And I'm sure there is plenty of debate to be had about "optimal" vs minor benefits. Let us not forget about the other 3 edges of the aquarium that are in constant contact with the water edge.. Maybe I should convert my tank into an infinity pool to prevent an algae inducing oil slick on these edges?

(I understood the 3ft comment regarding the weir length, but the drain isn't any
larger is it, nor is the return, irrespective of the weir length, so the quantum of water passing through is the same)

The point is.. A weir comb has it's uses and certainly does not alter the fundamental purpose of a weir nor does it drastically reduce the performance of the weir.

I'll leave it there. Happy debating. Peace.

 

[CuzzA]

Teeth on a weir is pointless and will not prevent an inhabitant from entering the box. Only covering the top of the box will truly prevent an inhabitant from entering. Nearly every fish will jump, some more so than others.

So since teeth do in fact cut the total surface skimming area of a weir in half and therefore decrease surface skimming by raising the water level above the weir and allowing water below the surface to enter the box they should be avoided. Instead there are many other ways to create a fence and completely isolate inhabitants from entering the box. The most simple being plastic gutter guard secured behind the weir and covering the top of the box.

But to each his own. I wouldn't do it that way on a custom tank and we can look at most stock tanks that almost always have a BP oil slick hanging at the top of the tank, unless of course they use powerheads to clear the surface, which then defeats the purpose of having an overflow to send crap to the sump to be filtered because they're just keeping the crap mixed up in the water column.

 

[Jay_R]

Comments all duly noted.

I have to state, that my weir comb has kept many a snail out, and the majority of my stock so it's far from pointless. The only fish that has managed the jump is my hawkfish, this is due their natural behaviour, which is to perch high ( i.e on my return nozzle, which is the location he jumps from ).

Otherwise, I have no protein to report and surface skimming remains unaffected, and all is well.

One point to note, teeth or no teeth, algae can and will still accumulate on the top edge of weir under the water flow, in the same way it can on on the return nozzle.