Help me install an overflow....

[Anonymous]

So I've just received a pair of internal overflows for my 125 gallon acrylic tank. I need to drill holes in the acrylic, and silicone the overflow to the tank. My only problem is that the tank is used, and therefore bowed a bit. There are tiny gaps, should I just throw on extra silicone here? Also, how exactly are the holes configured in the overflow box? The box is 6" X 6", with a 1" and 3/4" bulkhead...are they arranged diagonally in the square, side by side, etc? Is there enough room to fit a second 1" bulkhead in there?
Thanks ladies and chaps!

 

[Anonymous]

I can't help you with the holes, but I can tell you that silicone will NOT bond to itself if any part of it is already cured. You'll need to strip all old silicone out and replace with new. O! What FUN!

 

[Ben1]

I thought with an acrylic aquarium you need to use a special acrylic glue and not silicone at all. Sorry I am not much help other then that!

 

[ChrisRD]

Matt, are the overflows also acrylic? If so, you might be able to use a gap-filling solvent cement like Weld-On #40.

The silicone will work on acrylic for something "non-structural" like this (I've done it), but the solvent cement does form a much stronger bond.

As for the holes - I'd get the bulkheads you plan to use and make sure of the fit and arrangement before drilling anything...

 

[Anonymous]

Also, if I'd been paying better attention, I would have noticed that he mentioned something about the WHOLE TANK being acrylic.. wouldn't I? Hey.. I hope being worked up about a court date tomorrow is excuse enough. Sorry.

 

[Anonymous]

Huh? Please elaborate, SM!

 

[mhurley]

I hate to be a downer here, but:

1. Acrylic shouldn't bow. Even if it's used. That means the tank was underengineered when it was built. I've got an 8' long acrlyic tank and there no bow at all but it's made of 3/4".

2. If it bows now and the seams are showing stress (i.e. the gaps you are mentioning), that tank is going to eventually blow. I wouldn't trust it for anything except a 1/2 filled sump. Where exactly are you seeing these gaps at?

3. I wouldn't recommend silicone, especially if you're seeing signs of stress. Use either Weld-On 4 or Weld-on 16 to rebond the cracks. Use C clamps to hold it together while the glue bonds.

I've never dealt with aftermarket overflows, so I can't help you with those questions.

 

[ChrisRD]

Just to clarify Matt,

When you were referring to gaps I took it as gaps between the overflow and the side of the tank (since it is bowed). By "non-structural" I was referring to gluing overflow boxes inside the tank.

If you're going to be doing repairs to the tank itself I'd definitely use a solvent cement.

 

[mhurley]

Ahhhh...good catch....I might have missed that...I thought it was tank gaps...didn't think about gaps between the box and tank....
Still, if the tank is bowing, I wouldn't trust it...

Mike

 

[taikonaut]

>... Still, if the tank is bowing, I wouldn't trust it...

I never see any acrylic tank without any visible bowing when filled with water, <brag> and I see a lot of tanks <\brag>. It is just the material property of acrylic, and there is not much you can do about it except with a few exceptions. With proper material thickness, bowing is never a concern, but I do see some questionable ones with DIY tanks that were constructed with inferior stock.