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I was wondering if anyone knew how much pressure could be on the glass.

Also is there a better way than just leaning the rocks on the glass?
 

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if you put a rock in water you would find that the rock is not a whole lot more dense than water.

so the force that the rock exerts both downwards and sideways is not that much more than water.

so as long as the main vector force is downwards and the leaning force sideways on the back glass is just slight the tank shouldnt be exposed to a lot more stress than it would experience by just holding only water.

and in fact if a rock falls in water ...it is a much softer decent than in air like reduced gravity.

so the chances of it cracking the glass are much reduced.

thats why you should do all your rockwork in a full tank of water.
 

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avoid leaning rocks on glass, where possible use self supporting STABLE structures for your rock work.

ideally, make sure you have something under the rock to spread the weight, (I've used both eggcrate and slate roofing tiles) this stops any possibly dangerous pressure points (where the weight of rock is concentrated onto a small ridge or point of the rock)

with regard setting up the rock work, I wouldn't do it with a tank full off water, as this may make the rocks slippery I spent my time (carefully) placing the rocks in prior to filling. for instance, with my 180g, I actually stood in the tank to arrange the rocks, and I was using pieces of more than 50lb, this would have complicated the task if full of water.
 

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I generally keep about 160lbs of lace rock in my 75g tank. I actually have so much that I dont use it all and swap pieces from time to time..

I always have rock stacked against the back of my tank, but as stated its not much more pressure than the water exerts on it. I always try to have a stable "base" of rocks to stack onto but there is always rocks leaned against the tank.

I also beleive in arranging rocks in a tank full of water. They move much slower and should you drop one, or should one fall the chances or hurting the glass is very low compared to arranging them in air. I use eggcrate in the bottom of my tank for added protection.

As far as how much can a tank hold, you can fill the tank with gravel (assuming its in good condition), then add water and it'll be fine. Put in as much as you like.

 

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BurgerKing said:
I was wondering if anyone knew how much pressure could be on the glass.

Also is there a better way than just leaning the rocks on the glass?
No idea how much pressure can be on the glass. I think making the stand and tank perfectly level is every bit as important, I've heard of many more leaks from crooked stands than I have from rocks on the glass.

In my 90, I did a DIY background with the standard foam + concrete combo. It gives me a much more forgiving surface to lean rocks against. Makes piling up rock formations much easier.

My $0.03. (adjusted for inflation) :thumb:
 
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