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Re: Exploding glass, unven floors, 90 gallons, should I be

Sean Walsh asked if he should be worried about uneven floors and
whether he could tell if his aqwuarium glass was going to crack.

Well, uneven floors aren't a problem, but uneven tanks are. You should
shim your tank stand so that the tank is level when full.  Some tanks
will measure level on the stand empty, but when weighted down with
water and gravel will measure slightly off level (on wood floors). 
It's best to check with the tank full if you want to know how it's
going to sit.

Also, it's not how uneven your floors are but how stable they are?  Do
they bounce a lot when you walk around, do they sag noticeably more or
less when the seasons change?  A spongy floor, if it is wood, can be
braced and stiffened by a variety of sound methods.  If your concrete
is spongy, you more serious problems than potential cracks in glass
;-)Usually, abiding by building codes will be sufficient unless you
have a large tank -- 125 gallons or more, depending on a whole lot of
things.  A 150 gallon tank, filled can weigh about 1,800 pounds.  Put a
couple of people in front of the tank enjoying the aquascape and you
have over a ton on the joists! 

If you are concerned about a heavy tank there are some things to
consider.  The most important factor with the weight is the "stress in
bending" value for the joists.  If you're putting in a large or very
large tank over a wood floor, either consultant a bldg engineer or
brace amply from below, or both.  If that sounds too extreme, at least
consider how many tons will be resting over how many joists -- setting
a tank parallel to the joists puts the weight over very few joists. 
Setting it across the joists spreads the load and reduces the stress in
bending factor.  Consider how much other weight will be in the room at
any one time.  Bring a half dozen people into a room and you have added
about a ton of "live load" to the dead load of the floor itself!

Can you tell when a microscopic flaw in the glass will develop into a
broken pane?  For most practical purposes, no.  Which is why it's
important to avoid doing things that might cause cracks or unevenly
stress the panes.

Treated properly, tanks very rarely crack.  That's my story and I'm
sticking to it.

Scott H.

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