I had a similar thing happen to me on a tank I bought of Fleabay.

Except it was the front strutt that runs left to right.

I'd just set it up & was fillin it up with previous tanks water & it fell off.

I was well gutted!

I emtied it to about half way, till the front glass stopped bowing, found some thick tape & taped it front to back & siliconed the strutt back on.

Nearly cacked me self when it first happened though.

Good luck.

E

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3ft X 2ft Tank & 2 Small Quarantene Tanks

1 pearl Gourami 1 Sword tail
4 Upside down Catfish 2 Flying Foxes
1 Angel 4 Corys
1 Horse Faced Loach 1 Rainbow Fish
2 Congo Tetra's 3 Dwarf Suckerfish
3 Lemon tetra's 3 Red Phantom Tetra's
I Bristlenose 4 BN Fry
Plants

3 Lilly's 3 Onion bulbs
3 various other plants