Acrylic tank repair, ideas needed.

If you can hide that corner, use some 1/4" acrylic and rebuild the corner inside the tank, I would go about 1" past the damaged area. this will patch the weakened area but will show. hopefully you can hide it in the substrate.

I patched the bottom of a 100 Gal this way, something had been dropped in it and it had a 6" crack. it held for several years, then I sold the tank.
 
Theres no (easy) way to fix the outside corner of the tank, so I would do what bpimm said and cover the inside corner with 1/4" acrylic.
 
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