Is it true that glass tanks only need support at the corners?

[marino420td]

I have heard that glass tanks with plastic trim only need to be supported at the corners. I have a 120 gal (48X24X24) glass tank and I'm about to begin building the stand. I do not want a vertical support in the center. The 4 corner posts of the stand will be vertical 2X4's doubled and a 2X4 frame will sit on top of these post and will be covered in 3/4" plywood. Will this be ok?

 

[armygreen11]

Not the corners, the edges. The tank has to be supported evenly around its perimeter, in your case, the black plastic has to be supported evenly.

Your design sounds fine as long as it doesn't sag in the middle. You really don't even need the 3/4 ply. I'd lose the plywood and use 2x6's for the frame that the tank is going to sit on.

 

[theevoys]

The entire length of my tank on the back stick out about an inch from my metal stand. It has always made me very nervous... but nothing has happened to it. It's been 2 years (but I did buy renter's insurance).

 

[Scuba_Dave]

Depending upon your tank, having that plywood top could be a very good idea

If your tank has a flat bottom, then the plywood would support the entire bottom of your tank - and any rock work on it
In addition, if the bottom were to crack slightly, the plywood would support the crack
Without the plywood, a crack would become a catostrophic collapse

If your tank has a raised bottom, then the plywood will not support the bottom. But, it would help in keeping the stand together & adding to the overall strength

Also, if you will have equipment under the stand, it could prevent breaking the bottom of the tank from within the stand
Lifting something up & hitting the bottom of the tank from within the stand may be unlikely. But better safe then sorry in this hobby

 

[brian3]

From what I understand when talking to the tank manufacturers you are not supposed to completely support the bottom of the tank with plywood - only the outer edges / perimeter. They want the tank to flex in the center to prevent localized stresses that would occur on the crossbraces if supported.

 

[stugray]

If the glass is flat bottom ( no plastic trim ), then you should NOT use the plywood. You should try and support it only around the perimeter, and make sure the frame is level & co-planar.

If you put a flat bottom glass tank on plywood, then any point loading ( a screw not counter sunk ) will crack the glass once it is full. If you have the trim to hold the glass up away from the plywood, then it's Ok, just not required.

For Acrylic, it's the other way around. You want a flat bottom tank, and you want to support it evenly all across the bottom with minimum 'bumps'.

Stu

 

[cerreta]

I'm rebuilding my stand too and this info was very useful. Thanks all!

 

[armygreen11]

<a href=showthread.php?s=&postid=6725007#post6725007 target=_blank>Originally posted</a> by stugray
If the glass is flat bottom ( no plastic trim ), then you should NOT use the plywood. You should try and support it only around the perimeter, and make sure the frame is level & co-planar.

If you put a flat bottom glass tank on plywood, then any point loading ( a screw not counter sunk ) will crack the glass once it is full. If you have the trim to hold the glass up away from the plywood, then it's Ok, just not required.

For Acrylic, it's the other way around. You want a flat bottom tank, and you want to support it evenly all across the bottom with minimum 'bumps'.

Stu

Exactly.

If you really want the plywood, you need to put some foam on top of it to eliminate any point loading sources. Alot of people use that 1" thick pink sheet insulation. I'm going to use some thinner blue closed cell foam I found. It's alot softer than the pink stuff, but since it's closed cell, it won't collapse all the way. Should kinda make my tank "float" on the plywood.