Foam between my glass tank and metal stand or not?

[Cheebs]

I've had mixed opinions on this. I've a got a 75 gallon tank set up full of water, resting on a metal stand, with a 1/2" board of foam between them.  Everything seems fine, although the foam at the corners seems to have compressed a bit.  Anyways, I've got some people telling me that foam under a glass tank is not a good thing, I even had one person say it was a disaster waiting to happen.  Then others are telling me it's an important thing to have.  Any advice?

Thanks,
Cheebs.

[succinctfish]

Have a read of these previous OVAS threads, they should answer some of your questions.

http://ovas.ca/index.php?topic=12283.0
http://ovas.ca/index.php?topic=19416.0
http://ovas.ca/index.php?topic=19527.0

[Cheebs]

Hmm alright.. Thanks for that.  Not my only concern is that I've used the regular white foam underneath which isnt the suggested type.  The corners seem to have compressed a millimeter or two more than the rest.  Is this the result of the tank actually warping a bit from the stress on the corners, or is it because the stand is slightly imperfect/higher at the corners.

Thanks,
Cheebs.

[babblefish1960]

This difference in compression between the long edges and the corners point towards some of the dynamic expressions of the fluidity of glass when put in load.  The forces of water on the side panels is transferred to the bottom and these translate into slight changes in the shape of the bottom pane.

In short, this is the principle reason that the softer expanded cellular foam is passed over in favour of extruded foam such as blue or pink rigid foam.  This will still allow the tank to flex as it should, but with more resistance than the white foam.

Clearly I am of the camp that encourages the use of foam under tanks. I have seen a great many homemade and factory disasters over the years. It always seems to be triggered by stress risers caused by one of two things, an imperfect surface upon which the tank rests, and the other more common, yet less frequently understood cause, the uneven surface of an unleveled stand.  Good luck with your reading and decision.

[Cheebs]

This difference in compression between the long edges and the corners point towards some of the dynamic expressions of the fluidity of glass when put in load.  The forces of water on the side panels is transferred to the bottom and these translate into slight changes in the shape of the bottom pane.

In short, this is the principle reason that the softer expanded cellular foam is passed over in favour of extruded foam such as blue or pink rigid foam.  This will still allow the tank to flex as it should, but with more resistance than the white foam.

Clearly I am of the camp that encourages the use of foam under tanks. I have seen a great many homemade and factory disasters over the years. It always seems to be triggered by stress risers caused by one of two things, an imperfect surface upon which the tank rests, and the other more common, yet less frequently understood cause, the uneven surface of an unleveled stand.  Good luck with your reading and decision.

Thanks babble.  Here are a couple pics to help show what I mean.  Let me know if this worries you.  I dont have much int he tank so I have no problem draining it and puting different foam underneath.





IT almost seems curved..when I rest a straight board on the rim of the plastic frame aorund the bottom it's lower at the corner too.

[Cheebs]

I just  just took a level and started checking things.  I what I'm seeing is right, there is a very very small bow in the metal stand, and perhaps the foam is compression like this to even out the weight.. I also measured the angled of the plastic frame of the tank from the bottom, and everything seems to be level there... I'm still worried though.. I've jsut had to drain ym tank to add shims to level it off, it would be unfortunate if I had to do it again.. But if anyone thinks there is a danger if I don't than I certainly will.

Thanks Again,
Cheebs.

[mlee]

The bow in the stand is the result of the distributed load from the weight of the tank being reacted by the the support legs on either side of the stand.  The only way to minimize this would be to to have a third leg in the middle of the stand but this is not necessary.  There should also be a bow between the legs from front to back but this should be much less noticeable since the span is much shorter.  The foam is doing exactly what you want it to by evening out the load over the entire bottom edges of the tank.  If the tank were resting directly on the stand you would not have this bow but the the tank would be supported more at the corners (near the feet) and less in the center, possibly resulting in a cracked tank at some point.

I would ensure the stand is level and keep the foam.  My only concern with the white Styrofoam is that if it continues to compress over time the tank may migrate towards the front, back, left or right (depending on how good the level is).  Looking at your pictures though...I think it will be fine.

Mike

[Cheebs]

Thanks alot Mike, and everyone else.  I've actually drained my tank once already because of unlevelness, and everything is shimmed and perfectly level now, so I should be safe.  Thanks again!

Cheebs.