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CUTTY
10-14-2003, 02:19 PM
Hi all i just have a quick question for you all i was wondering how much wieght can the bottom glass of a 55 gallon aquarium hold up without it breaking because my rocks are river rocks they are smooth but the are heavy and i wont to take my rock work all the way up the back to the waterline so if anyone knows how much please let me know thank you.

SGypsyMermaid
10-16-2003, 10:16 AM
i'm moving this to 'equipment & water chemistry' forum.

tom
10-16-2003, 11:46 AM
Cutty

The only definitive "answer" would be "depends" (on the properties of the glass and of the base, weight/resistance of this and that, etc.), but I'd be more concerned about a rock falling and breaking some part of the glass more than I would the weight.

Here's why:

Figure a 48 x 13 x 19 ( in., approx) volume of water weighs around 200 kg (I'll just use metrics from here on--it's easier and conversion tables are plentiful). We then get F/A (Force/Area) of about 50g/cm2. That's only around .7 psi--very little pressure.

Let's say your rocks have a density of 3 x water, or simply 3, and let's say you have rocks all the way up to the top of the water level and covering, at their base, around half of the tank area, and at their highest point of 48cm (the 19" height) around an eighth of the area.
That's still only around (a real approximation here, but fair) 125g/cm2, or about 1.8 psi at the greatest point. (Someone check my math, please.)

If the bottom of your tank sits flush level on, say, a solid oak stand on the first floor, you couldn't put enough smooth rocks in that tank to break its bottom--at least not by their sheer weight.


Note to science teachers/students: I'm using specific gravity and density interchangeably, and I'm not considering whatever slight variations owing to temperature and stuff. But that's ok, right? :D

chc
10-16-2003, 04:35 PM
The bigger thing to consider is the distribution of the rocks on the pane of glass. A heavy rock with a sharp corner can do a lot of damage whereas several VERY heavy flat rocks may cause no trouble at all.

It is usually wise to place something on the bottom of the tank to better distribute the weight. I use sheets of styrofoam (Home Depot, etc.). In very heavy situations, I use a layer of egg crate and styro on top of that.

Also, it is important to put s piece of styro under the tank itself to help level and stabilize the whole thing.