Fixing a leaky tank is very easy. You can get tanks pretty cheap a lot of times because they leak and "are only good for reptiles". First you will need to purchase a razorblade scraper from your local hardware store. They are cheap, usually $1. Cut along the seam of silicon on both sides and it will pull right out. The corners are a little more work, but it's not that hard. Now keep going over the seam to remove all the silicon. Now get a damp rag and clean the seams very good. You can also us an alocohol wipe, just make sure to wipe with damp rag to remove any alcohol. LFS carry silicon but charge an arm and a leg for it. Go to the hardware store and buy a tube of GE Silicon ONE. Make sure it is ONE not the TWO. The Silicon I comes in blue tube, the 2 comes in brown tube. Now start in the corner and start your bead, and be liberal on the silicon, especially the bottom seam. That gets covered with gravel anyways and wont be seen so that one doesn't have to be pretty. After all seams have nice thick, even bead, wet your finger, or you can use a spoon, and run it gently down the seam to spread it out. Let it cure of a few days and your good to go.

To get a perfect seam use painters tape and mask the edges if your joint and after you use your finger/spoon remove the tape. This takes a little more time but looks tons better. Also make sure you do get 1 and not 2 GE Silicone and make sure if you get a replacement there is no mold killer

great tip on the tape Dan!!!! Awesome idea, and I will make sure to do that on a 20 that Tasha gave me!!

you can put acohol on your finger and it will not stick to it cause do that all the time for counter tops since i work a granite shop hope all these info helps out