150 gallon aquarium with a crack.?

Yes. First, remove the top molding by cutting it loose with a razor blade. Make sure the bottom is clean and grease and acid free, Use an alcohol swab to clean the joints. Place the new glass on the old. If you patched the old crack, make sure you cut the old sealant off SO it will be perfectly smooth.

After you put the new glass in and are certain that it is flat, clean its edges and then but a large beard of aquarium silicone (use a gun) in a continuous bead. Then take your finger and gently press the silicone into the joint with even pressure all the way around the bottom. Reattach the top molding with a little silicone, Give her a few days to cure and you should be in business.

After saying all that, most glass companies will repair it for you for a reasonable price.

Once the integrity of the aquarium is compromised, it is prudent to throw it away. Even with an additional piece of glass on the bottom and well sealed, it no longer has the structural strength to hold the water pressure (hence the leak continues). You don't want to take the chance as to when it will start to leak again (for example: 2 months after you have set it up and put a few hundred dollars into decorating and stocking it). Remember the weight and pressure that these tanks need to hold in order for them to retain the weight of water (1 gallon = 10 pounds). Even if the seal held, the fact that the original tank has the cracked bottom, it may produce another crack on one of the glass walls, if it shifts due to the weight. Wish there was better news, I found out the hard way! Good Luck!

It may work, however you may not be able to fit the right size piece of glass into the tank. The frame around the top of the tank will likely cause a problem.

You already have some good answers. I'd just like to point out (from sad experience) that if you don't fix it right, 150 gallons of water makes quite an amazing mess.

that should work if you get it clean and your measuring is right on get some good water or aquarium sealant that should fit it thro it would make heavy.... but for that price id do something forsure hey heres a site that might help they know so much about fish keeping http://www.oscarfish.com/

You can try that. You can also purchase glass repair sealant and apply it to the crack also.