Foam under tanks?

[Quatro]

Hey, I am wondering the correct placement of foam under a tank.  I was just looking at Brine's sturdy new stand and noticed that he cut his faom larger then the footprint of his tank while I have cut my foam smaller then the footprint.  All the weight on mine is on the bottom pane of glass (ie.  the black trim is about 1/4" above my stand.  Just wondering if there are pros and cons to each way or if one is better.

[babblefish1960]

With a lot of modern aquariums, you will find that the bottom pane of glass actually floats off the bottom surface, about an inch I think. In these cases, the styrofoam needs to be completely underneath the tiny plastic perimeter in order to remain stable.  In Brine's case, the tank bottom is the glass, so the entire surface of the glass is supported by styrofoam.

I have seen a badly placed bit of styrofoam under a rather large floating bottom pane tank, allow the ever wobbling tank to slip one side completely off of the styrofoam, and believe me, it is a very scary thing. It fell off, a catastrophic situation, but an extremely buckshee arrangement all around, so I would call that a worst case scenario.

Moreover, if one side of the tank has less equal pressure resisting its weight from beneath, it could cause undue flexion in the larger front or rear panes, and this as you know causes stress risers that will ultimately cause the glass to break, as in the case of busdriver's 150 gallon.

Be a good lad and consider breaking the tank down and setting it up all over again to be absolutely certain.   You weren't doing anything else anyway.

[Quatro]

I don't really see the difference.  If you have a flat bottom tank and can safely put it on foam why would it be unsafe to cut the foam slightly smaller to put it against the flat bottom of a recessed tank?  I think back to the discussions about stands with legs, how people suggest a flat bottom to distrabute the weight.  Isn't it the same with tanks?  If I cut the foam larger then the footprint, all the weight would be on the edges of 4 panes of glass.  The way it is now the weight is of the entire 48x18 footprint.  Heres a pic to make sure we're on the same page.


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[babblefish1960]

Nice try there big fellow, I can see your logic in thinking that you have done the same, however, as the tank is filled, the panels are bowed outwardly on all four sides at the top. And with a floating bottom, this is accounted forby allowing the reverse bow, (inward bow) to take place without interference. When the inner space, or void, underneath the tank is filled with rigid foam, the action that then takes place is that the foam treats the flexing glass as a lever, and the floating bottom is no longer a fulcrum, the foam is, and then there is tension shear along the upper silicone seal on the bottom pane and eventually, you will have a leak as the silicone weakens.

Now, having said that, we are talking about very small movement, and of course, a long time. Additionally, this presumes that the styrofoam is very close fitting underneath the tank inside this void.

On the other spectrum, a floating bottom pane is meant only to resist the downward force of the water and nothing else, whereas the earlier versions of tanks required the bottom pane to carry the weight and stress of everything above it. In this way, manufacturers have been able to reduce the thickness of the bottom piece of glass in floating it independent of any other static and dynamic forces to do with the aquarium.

So there, you've been told, when you support a tank on its floating bottom, you change the intention of the original design by introducing new forces the designers figured out how to avoid dealing with.  In short, it may eventually break if it doesn't leak first.

[Quatro]

Great.  Now I won't be able to sleep tonight. 

It has been setup like that for almost 2 years and no problems so I won't worry too much.  I was planning on redecorating someday so I'll fix it then.

Babble, once again your verbose responses and complicated terminology has brought me to my senses.  Thanks   

[babblefish1960]

Why thank you Quatro, I should like to add that these forces only really become a serious concern when dealing with the larger family of tanks.
Up to a 3 foot length, I wouldn't get your knickers in a twist over it, but once you get to 3 feet and longer, and most especially when it is 18 inches front to back or more, and as well, 2 feet tall or more, do these forces become something that cannot be ignored.
Everyone has an ancestor who drove a model T Ford with hay bale wire to hold it together and home made hooch to keep it running, but it is not always the best situation.

[darkdep]

I would second a lot of what babble said, but without the babble.  Tanks were designed to be supported by the edges, unless the edge glass is sitting ON the bottom glass.

What's the size of the tank we're talking about?

If it's sat for 2 years, it's not likely to break anytime soon tho. 

[Quatro]

Its a standard 75gal.

[freshwater]

How interesting! So is foam under the 4 edges necessary?

[babblefish1960]

Oooh, a four footer, not good in the long run, mind you, people have done worse and managed to get away with it.  And yes, the foam is necessary under all four edges.  And just a reminder that foam doesn't make the tank level, a level stand does, foam just insulates the tank from stress risers by allowing imperfections in the stand to be absorbed.

[PineHill]

If the tank does have a floating bottom, is it essential to place foams underneath it?  And what are the risks if not place and benefits if placed.  Thanks

[darkdep]

No, you don't need foam under the floating bottom.  No risks whatsoever.  It's technically a safer design; I'm sure lots of tanks with solid bottoms were placed on a stand with an accidental piece of gravel or something underneath that ended up cracking the glass.