How many pounds of rock can a fishtank hold?

[Chick-In-Of-TheSea]

Not gravel but large rocks.  Is there some sort of rule?  Pounds per gallon or whatnot?

[The endler guy]

in reefing it is suggested you keep 1 lbs of live rock per gallon but that is for filtration, i assume you could fill an aquarium with tungsten and as long as the thing the tank is on is fine you should be ok (in that scenario the glass bottom would probably brake but I assume you arent filling an aquarium with tungsten! at least I hope ;) 

you have to remember that water is very heavy 1lbs of water= 16 oz and 1 gallon is ~8 lbs and one square foot is ~5lbs (tmi water is heavy!!!)

[lefty o]

it will hold at least an amount of rocks equal to the weight in water it will hold. biggest issue with big heavy rocks is that they can bear all the weight on a small contact point if they are placed directly on glass.

[Chick-In-Of-TheSea]

On 11/2/2022 at 6:33 PM, lefty o said:

it will hold at least an amount of rocks equal to the weight in water it will hold. biggest issue with big heavy rocks is that they can bear all the weight on a small contact point if they are placed directly on glass.

What if they are placed on substrate (ie: sand)?

[The endler guy]

On 11/2/2022 at 6:36 PM, Chick-In-Of-TheSea said:

What if they are placed on substrate (ie: sand)?

i assume you would be fine (the old ladybird 800 had many rocks and was fine if I remember correctly) 

personally I would worry more about what the aquarium is on then the aquarium its self

and if you are realy worried (and building the tank) make the bottom thicker/ out of a stronger material and make sure to distribute the weight 

Edited November 2, 2022 by Aiden Carter

[Chick-In-Of-TheSea]

On 11/2/2022 at 8:50 PM, Pepere said:

Rocks weigh about 157 pounds per cubic foot. Varies according to the type of rock.

water weighs about 64 pounds per cubic foot.

now it gets interesting.. if you submerse a cubic foot of rock that weighs 157 pounds when dry under water in an aquarium, you add 157 pounds to the aquarium, but if you are holding it off the bottom with a spring scale, it will weigh about 93pounds.

the weight of your rocks bearing down on the glass will be less once you have water filling the tank. The tank however will weigh more with rocks and water in it than just water in it. 
 

work at wrapping your mind around that….

 

That makes total sense to me. Like how a person can lift up another person in a swimming pool. 

[lefty o]

On 11/2/2022 at 5:36 PM, Chick-In-Of-TheSea said:

What if they are placed on substrate (ie: sand)?

that works great to help spread out the weight.

[The endler guy]

On 11/2/2022 at 8:50 PM, Pepere said:

Rocks weigh about 157 pounds per cubic foot. Varies according to the type of rock.

water weighs about 64 pounds per cubic foot.

now it gets interesting.. if you submerse a cubic foot of rock that weighs 157 pounds when dry under water in an aquarium, you add 157 pounds to the aquarium, but if you are holding it off the bottom with a spring scale, it will weigh about 93pounds.

the weight of your rocks bearing down on the glass will be less once you have water filling the tank. The tank however will weigh more with rocks and water in it than just water in it. 
 

work at wrapping your mind around that….

 

ahhhhhhhhhhh physics i hate it : (