Kessil

Tank is 1/2" Uneven

Schmuck-Reefer

Supporting Member
Hello Everyone,

Im in the process of setting up a new tank. Its a 180 Gallon peninsula, 60"x30"Wx24"T

Anyway Ive got it placed where I want it, and the tank is not sitting perfectly flat. Infact its just under .5inches off at each end. This is an aluminum stand with suports in each end and in the middle. Im worried if I just shim one side the middle supports will be no longer in action.

Also the floor is a concrete pad.

Appreciate any suggestions.
 

sfsuphysics

BOD
Staff member
I assume you used a bubble level to see that the stand is not level, but you might want to make sure the legs are also not level, because if the legs are level and you shim the stand you're going to end up putting the legs crooked which would put an unwanted strain on the stand.
 

Flagg37

Supporting Member
Look for the composite shims instead of the wood ones. They won’t deteriorate over time with exposure to saltwater.

Getting spilled water out from under it will be difficult. What kind of floor is that under it?
 

ofzakaria

Supporting Member
I always shimm. Ad a matter if fact I start with tank empty and shimm, then fill tank half way, give it a day to settle then adjust the shims. It's almost always, the tank settle and require bit more adjustment when its filled with water..
Am assuming you are using air bubble rod that is biting enough to evaluate the leveling. I use a long rod that is 6 feet so I get accurate leveling information.
Indeed use composit shims it's way better than the wooden one that eventually rot
 

JVU

BOD
Staff member
One good way of checking level with 100% accuracy in all directions is to put a very small amount of water in the tank, just enough to form a level where it’s almost touching bottom glass on the high side. Also allows you to see exactly how far off you are and when you have it level.

Since your bottom is flat I’d use multiple shims, at least 1 under each of the low and middle posts.
 

Flagg37

Supporting Member
I don’t know how perfect you want to level it but I’ve used a marble in the tank (while it’s empty). It will roll in the direction that needs more shimming.

What is more important than being level is being flat. If the tank is 1/2” out of level but it’s perfectly flat it should be fine, but if there was a single corner that was 1/8” too high, it will likely fail eventually.
 

Bruce Spiegelman

Supporting Member
Ok -- so I really need to correct something here. This idea that more pressure is exerted on the seams or glass of a slightly uneven tank isn't really true. My 6" tank was off by an inch for many years. During that time I researched the issue just to satisfy myself that there was no problem. Here's the easiest way to think of it. Water "exerts" pressure equally all around. Not more pressure on one side than the other. So even if the tank is slightly off the pressure is still the same. It doesn't exert more force on a corner. It's the same pressure pushing outward all around. Now in order to be 100% certain on this, and to explain it better than I can, I asked a college buddy who teaches Physics at the University of Texas to explain it. Here's the science:

"Pressure increases with depth, but at the same depth the pressure is the same. P = Patm + rho*g*h Atmospheric pressure is 101,300 N/m^2 Rho = density of water (1000 kg/m^3 for fresh or 1025 kg/m^3 for salt) g = gravitational constant = 9.80 m/s^2 h = depth in meters"

The pressure of an extra inch of "depth" is negligible so pressure on the 1" lower corner is the same as it is on the other corners. .
 

svreef

Supporting Member
But gravity is always pushing down...so a mass that is tilted will have more force exerted on it at an angle - like a car going uphill.
 

Coral reefer

BOD
Staff member
It would certainly worry me more with certain tanks than other. Say a no over built rimless glass vs. acrylic.
Seems like flat is more important than perfectly level, but I would absolutely try to get a new install level if at all possible.
 

Coral reefer

BOD
Staff member
Ok -- so I really need to correct something here. This idea that more pressure is exerted on the seams or glass of a slightly uneven tank isn't really true. My 6" tank was off by an inch for many years. During that time I researched the issue just to satisfy myself that there was no problem. Here's the easiest way to think of it. Water "exerts" pressure equally all around. Not more pressure on one side than the other. So even if the tank is slightly off the pressure is still the same. It doesn't exert more force on a corner. It's the same pressure pushing outward all around. Now in order to be 100% certain on this, and to explain it better than I can, I asked a college buddy who teaches Physics at the University of Texas to explain it. Here's the science:

"Pressure increases with depth, but at the same depth the pressure is the same. P = Patm + rho*g*h Atmospheric pressure is 101,300 N/m^2 Rho = density of water (1000 kg/m^3 for fresh or 1025 kg/m^3 for salt) g = gravitational constant = 9.80 m/s^2 h = depth in meters"

The pressure of an extra inch of "depth" is negligible so pressure on the 1" lower corner is the same as it is on the other corners. .
Out of curiosity wasnt this the same 6’ tank that coincidentally wound up having a seam fail? If so was it on the side that was lower than it should have been?
 

JVU

BOD
Staff member
But gravity is always pushing down...so a mass that is tilted will have more force exerted on it at an angle - like a car going uphill.
Yes that is the common misconception. Fluids don’t work like that though.

The force of gravity is exerted as a pressure that pushes in all directions equally for any given depth. The actual force exerted is the pressure (depth) times the surface area of the wall, without regard to which way is down. So a larger panel has more force pushing on it, but it doesn’t matter if it’s the bottom or the side at a given depth.
 
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