Hi redoing the silicone on a Tank is not that hard I do it when I get a used one. Home hHardware carries the right silicone just ask the people at the paint counter they will find it you have to tell them it it for an aquarium buy the large tub the one that gose in to a chaulking gun. There is 3 ways to R&R silicone on a tank. first make sure you know exactly where the tank is leeking.

1. Using a raser knife or one of those retractable knifes cut off all the silicone on all contacting serfaces. Pat extra attention when cleaning off the glass to not scratch it.
Where the leek is you will have to cut a bit of the silicone out from between the two glass surfaces. Be very carfull to not chip the glassdo not force your cutting edge in between the glass. This the second resone why you want to use a rasor blade it is very thinand can get a thing wedge of siscone out . You do not have to get 100% out as if it is stuck and dry the new silicone will stick to it. you only need some to get in there to creat a new bond that will hold the 2 pieces together. Remebmer the silicone that is on the inside of the tank that you smooth out is what holds your tank together mostless or gives the bond the strenth. Once you have cleaned all surfases and they are completely dry as silicone will not stick to a wet surface. You then need to start replacing the silicone take you gun and start laying down the silicone I do the bottom first and then the coners doing the one that leaked last. Now you need to use a corner tool don't press to hard you want a nice wide round corner the wider the better for strenght this is what keeps your tank from comming apart. I do the bottom last as it dose not have to look prity but it still has to be done. let it cure and after it cures then do the edge around the black trim stops salt creep.
This is my prefered way to repair a small leek.

2. You can remove all silicone from glass all sides and then remove the one pain of glass that has the leak and then redo the silicone. be extra carfull because to remove the pain of glass it is very easy to chip it. you will have to work from the inside of the tank and the out side. You will have to cut the silicone bead all the way throught on all sides you will need some one to help you with this. You then will have to clean of any excess silicone and replace it all at one time. Make your corners nice and round; every where the two pieces of glass meet is a corner.

this method is better and will not leek there again.

3. you will have to take your entire tank apart. LOLOLOLOLOL. I do not recomend doing this but you can. Once you have cleaned off all the silicone start putting it to gether. If you make a jig it will be much easyer. take two sides and silicone the mating edges put them together now take anouther side and silicone it and put that one in place making sure that it makes contact with the edges of the first two pieces.

Do this on a flat surface.

so first bond the bottom and one side.
next take a second side that meets the other side and bond the three pices to gether.
then take the opisit side from the one you started with and bond that one.
Then take the last side and dond that.

You then will need the silicone the inside of the glass all of this has to be done in one easy flowing continual step. Once the inside is siliconed then make your round corners.
Once all the siliconing is done all pieces of glass have to be held in place till silicone is set and strong enough to hold glass by it's self. Once silicone is cured trimm all excess of the out sid of the tank and then put your trim on.

This is not my perferd way of repairing a tank.

I have built them this way though. Remember to make a Jig, take measurments of the outside of your tank before you dismantal it, this is the best way to do this job. You will only need the help of one freind then and you can enjoy a cold beer while the silicone cures.

BY the way you will need a few very good freinds to do this if you dont have a jig.
But once you have done this you can make your own tanks, It's not that hard just a learning curve.

I hope this helps.
Bill