Tank crack patch

[bounce]

Today I free listed a 70gal that has a "u" shaped crack along one of the long sides. They said it won't hold water on the listing but I went ahead and got it anyway thinking I can repair it.
I have a large piece of glass from another aquarium I can use to patch the crack from the inside and I also have an enormous excess of acrylic.
Has anyone ever patched a crack in a tank before? Any advice... Best to use glass on the inside and acrylic on the outside? does it matter how thick the glass is?
I eventually want to fill it with some critters (frogs or other fun amphibians) permanently, but for now I just want to get it holding water to do some aquaponics experiments with talapia and a rain gutter I also got for free today to hold some hydro plants.
Its also great to think about the possibilities, what can this size tank house?
Thanks

[Mentat]

Don't think you can patch a crack in a tank to hold water. The only procedure available is to remove the broken glass, scrape off and remove all old silicone, clean area to be glued with solvent (can't remember exact name right now; maybe acetone); re-apply new aquarium silicone; and replace glass. Some tanks have one or more tempered panes; but if your's have crack imagine it's not tempered. Also, you might be required to remove the top and/or bottom plastic frames to complete repair. It's a time consuming procedure and has to be done with gloves (to protect against cuts, solvent, and uncured silicone) and in a well ventilated place. Good luck !

[mats]

I have successfully patched terrariums and made them waterproof again. both side panels and even bottom. The side panels are pretty easy. I just scraped off enough silicon to get the fit as tight as possible and then I put jesustape as we call it (roadietape or duct tape) on the outside to keep the cracks in place, then I just siliconed the new glass to the side both framing the pane and criss crossing it. I used some duct tape and a rather large stone to keep the pane in place while drying. Later I siliconed it from the inside to make sure it was tight and presto! As good as new.

On the other tank where the bottom went crack in the night, I ordered a new pane cut to fit inside and did the same procedure. working well still ( keeping in mind that I have about 8 cm of water covering the bottom of a 60d 95w 70h tank...)

[bounce]

I am hoping to patch it as you described! I found a video that shows putting the silicone over the crack instead of a criss-cross to get the crack repaired and covered, and then going over the perimeter of the patch piece to seal it in place.
I picked up some "100% silicone" yesterday, its black in color and says its food safe, so Im imagining this means frog safe too, but odd it is black.... It says it is waterproof but also says its not recommended to be used exclusively under water, so I'm not sure what they are getting at but for $5 I'll try to get the tank working again. ...And put the ugly black patch side on the back.
The alternative of replacing the enormous piece of glass that has a relatively small crack in it seems a waste of money. I would need a piece that is ~3.5/4ft by 1.5/2 ft Not sure the cost on it, but if its over $20 I'm stingy and will attempt another way to fix it, if I invest more it becomes more of a surgical procedure instead of a free adventure if you will.

Thanks for the advice for the plane replacement method none the less, definitely want to make sure I've got the right ideas going.

[mats]

yes, well, putting the silicone over the crack on the inside was so plain for me I didn't mention it, the tape went on the outside naturally. the crisscrossing was more important when I did the bottom, as it takes away tension that otherwise might crack it again.

Good luck!

[bounce]

okay that makes sense, makes me wonder what other designs could be used to resolve the tension away from the crack.