How strong is our glass tanks and can withstand the weight?

[jcarson]

Hey gang not sure where to post this so here it is....

I have a couple 55g tanks of standard dimension retangular tanks 5' long x 12"deep x 20" height and 1/4" thick glass .

My concern is can I place large rocks that weigh in excess of 20-30lbs directly on the glass?

Will in not cause a stress points where it touches the glass and cause it to start cracking?

I have a similar capacity tank and have used egg crate to "cushion" or distribute the weight but notice gravel gets stuck under the egg crate and I am concerned that this may create a stress point.

Can someone set my mind at ease?

 

[markstrimaran]

Multiple 30 pound rocks?

 

[A201]

This is a hardscape I had going a couple of years ago. It included well over 200 lbs. Of rock. The base rocks all have flat bottoms. No egg crate, just a couple of inches of small grain gravel.
As long as the rocks have relatively flat or smooth rounded bottoms, no problems on bare glass.
Glass is unbelievably strong as long as the weighted objects are sensibly distributed.

 

[fishhead0103666]

I once used an old 10 gallon to show off this small boulder I guess you could call it I found. The bottom didn’t break.

 

[RD.]

I recall a rep for one of the larger aquarium distributors filling a 75 gallon full of large boulders. Full as in up to the brim, just as a demonstration of how much weight a glass tank can safely hold. No egg crate, no problem, as long as the boulders don't come crashing down.

The tank below isn't mine, but I saved this image many years ago as an example of what I thought was a well scaped mbuna tank.



One thing that I will caution you about, many of the bottom panes of commercial tanks are made from tempered glass. A single sharp point of pressure can potentially cause disaster, so while weight of rocks isn't an issue, a sharp piece of gravel, causing stress in just the right manner, under that weight, could cause the tempered glass to shatter.

 

[RD.]

Below is a pic of one of my 125 gallon African tanks from years back. The rocks weighed approx. 225 lbs in total, and were placed directly on the glass, with the sand added after. It sat like that for close to a decade, no problem. And the bottom of that All-Glass tank was tempered glass.

 

[jcarson]

Multiple 30 pound rocks?

Yes sir multiple 20-30lb rocks

This is a hardscape I had going a couple of years ago. It included well over 200 lbs. Of rock. The base rocks all have flat bottoms. No egg crate, just a couple of inches of small grain gravel.
As long as the rocks have relatively flat or smooth rounded bottoms, no problems on bare glass.
Glass is unbelievably strong as long as the weighted objects are sensibly distributed.
View attachment 1342041

Thank you

I recall a rep for one of the larger aquarium distributors filling a 75 gallon full of large boulders. Full as in up to the brim, just as a demonstration of how much weight a glass tank can safely hold. No egg crate, no problem, as long as the boulders don't come crashing down.

The tank below isn't mine, but I saved this image many years ago as an example of what I thought was a well scaped mbuna tank.

View attachment 1342052

One thing that I will caution you about, many of the bottom panes of commercial tanks are made from tempered glass. A single sharp point of pressure can potentially cause disaster, so while weight of rocks isn't an issue, a sharp piece of gravel, causing stress in just the right manner, under that weight, could cause the tempered glass to shatter.

Below is a pic of one of my 125 gallon African tanks from years back. The rocks weighed approx. 225 lbs in total, and were placed directly on the glass, with the sand added after. It sat like that for close to a decade, no problem. And the bottom of that All-Glass tank was tempered glass.

View attachment 1342061

Thank you for putting my mind at ease.

I was actually thinking of running thick beads of silicone all across the bottoms of the tanks to form a cushion but this probably is overkill reading your replies.

 

[fishhead0103666]

If you really wanted to overkill then you could get a huge slab of rock and cut it to size so it covers the bottom of the tank.

 

[RD.]

Thank you for putting my mind at ease.

No worries, glad to help. Just be careful when initially placing boulders in glass boxes.

 

[skjl47]

Hello; I can recall a couple of posts where the bottom of tank was busted with rocks. In one it was when the rock was dropped a short distance when being placed. The other was when a rock apparently had been stacked on top of others and somehow fell from it's position onto the glass bottom.

A thing about tempered glass is that it does not crack like plate glass and then leak out slowly. If it breaks then it goes all at once. The entire sheet of glass shatters into small pieces about the size of grapes.
If I had to have rocks placed on glass then I would consider some sort of layer on top of the glass. Maybe a sheet of acrylic or some such to spread the point of impact out a bit. When I managed to shatter a sheet of tempered glass it was at a very small point. I think the glass in car windows can be shattered with a pointed tool but may survive more blunt blows.