Oh No! A Crack!


New member
Following this thread I built a horizontal external overflow in a 75gal bowfront: http://www.reefcentral.com/forums/showthread.php?s=&threadid=444094

The cutout looks like this pic:


I was rearranging my rockwork this morning and when I pressed the powerhead against the back wall this happened:


What do I do??? There is water and fish in this tank... Will silicone work and how? Do I put another piece of glass over the area as a replacement and reinforcement?

Aqua Keepers

New member
Notice that in the link you provide he does the cut outs on the short end of the tank? Thats because there's not as much pressure or flex to those shorter pieces. The back wall of a 75 is kind long and is more prone to crack with this methode. When doing this on a long pain of glass as you did, you need to add some sort of braceing under the cutouts. Usually the piece of glass you cut out would work as a brace.


New member
You should have 0.500" corner rad there as well. Or you can use a quarter coin for guideline of 0.500" corner rad.

The link provided didn't even have a rad in the cut. It will soon crack it's a matter of time.


Premium Member
I'd say that:

non-linear catastrophic structural exasperation is imminent.

Meaning - drain the tank & replace it.

Sorry that's not what you wanted to hear.

To get by overnight, I would clamp two pieces of glass ( one on each side ) with silicone in between and some rubber feet clamps to hold it in place. Make the pieces extend a few inches beyond the crack. They can cut these for you at Ace hardware.

That is only a temporary fix ( 1 or 2 days max ) until you find a replacement tank.



New member
Well, all I can say is that all these other guys here who are suggesting you replace the tank are just talking theories, and probabilities. MY suggestion that you replace the tank right now, comes from personal experience. Consider yourself VERY lucky that what happened in my case didn't happen to you. The crack in my case, ran from that corner, all the way down to the lower opposing corner in a 125. It just blew out as though someone had thrown a brick against the tank. Through some dumb stroke of luck, my son and I were in the room at the exact moment it happened, and we were quick enough to stick two mag drives in there and get most of the water pumped out a nearby window, but what a mess. Pito is absolutely correct. Those slots are safest to cut into the side panels of larger tanks. I wouldn't even waste time patching it. Bit the bullet, and replace the tank. Besides, you'll never find a better reason to upgrade.


Premium Member
My Soap Box 2 cents:

Thread after thread, I see folks using a dremel to hack out holes and slots in their glass tanks. In each and every case it is a disaster waiting to happen. The cuts are rough and full of thousands of cracks and fissures.

If a dremel is used, the remaining edges need to be eased and polished to remove the rough areas and eliminate the stress points and sharp corners.

As mentioned, the corners need to be radiused. A corner is a place for stress to focus and start a crack.

The safer bet would be to have your local glass shop cut the slot for you. They will be able to radius the corners and eas all of the edges.

There is no question that the tank needs to be replaced.

bad santa

SCRK member
you need to replace the tank (maybe time to upgrade to a bigger and better tank) or buy a shop vac and have it readilly available.