I want a 125 gallon, it is on cheap at a Frenchy's store, but it hasn't had water in it for a few years (used to house a boa). The glass is really thick, probably3/4 inch, and besides chips in the corners, there aren't any cracks.

It will definately have to be resealed, so I strip the silicone with razors, do I remove it from the outside edges too? Or just run a new bead of silicone along the outside? Should I do it one seal at a time, waiting for the silicone to cure fully until I do the next one?

And generally, what should I look out for in a big tank that's second hand? The lady won't give me any sort of guarantee.

Thanks for the help!

I repaired a tank several months ago and used a razor blade to strip the silicon bead from the inside of the tank being careful not to get the blade in between the two edges of the glass.
I then used a good quality aquarium silicon to re do the beading. One of the corners was chipped so I used a small 2" x 3/4" piece of glass and siliconed this in the corner on the inside of the tank. This whole operation was done in one go to avoid joins.(Hope I make sense).
I did not touch the outside of the tank.
Generally what to look for would be chipped corners or badly scratched glass. Algea seems to really stand out when growing in the scratches!
Corner chips can be repaired as mentioned by siliconing a small piece of glass to the area on the inside of the tank.
Another factor would be the cost of the tank. If very cheap it would be worth repairing.
If after all this restoration work you have no success (but you will I'm sure) you can always buy some pet mice to keep in there.

Great advice, not sure what you meant about avoiding joins, but I got the 'all in one go' bit
The chips aren't too bad, not very deep, just unsightly. No scratches, which is pretty good

it's $195 CDN for tank and metal stand, she won't give it to me for a lower price because she swears that's what she paid for it, yeah right <_<

so it's pretty unlikely that when it's filled with water, a pane of glass will explode?

Don't know whether that price is cheap or not in your country. If you are at all unsure about the purchase, give it a miss. I'm certain that you will have many more opportunities in the future to purchase aquarium equipment without worrying whether you are doing the right thing or not.
By avoiding joins I mean that if you finish a run of silicon and let this dry, then when you start again from this point, you have in fact got a joint, even though the two materials are the same(silicon to silicon). Even this will be okay if you "overlap", but I like to try and complete a job when opening a tube of silicon.(These things have a habit of drying out on me, a little bit like half used tins of paint!)
The worst scenario is when you have to replace any of the glass completely.You will then need to cut, or have a new pane cut for you to a pretty exact fit.
Do the four vertical edges of the tank have any plastic covering? By this I mean strips of plastic angle material?
I generally purchase several meters of plastic angle (1/2" x 1/2") and silicone these to the vertical edges for protection. (Cut to the right length of course)
Most chipping to tank corners and edges can be avoided by the use of such plastic angle.
Do not silicone these angle strips to you tank untill you are completely satisfied that the tank does not leak.
Please keep us informed.

That size tank is impossible to come across in this province, unless you built it yourself. I would say that for the size and glass thickness, that it is a pretty good deal. it also comes with a wraught iron stand and a nice background, although I'm probably going to make my own stand!

The edges do not have the plastic edging, but I know where to pick that stuff up when I'm satisfied with the sealing job. Can I silicone them to the edges when the tank is full of water?

I see what you mean about avoiding joins now. I'll give them a call, and see if the tank is still there. Likely it is.

How did you go with the tank? Yes, if you are going to add the plastic angle to the vertical edges of the tank you can do so if the tank is full with water providing the area to which they are applied is dry( should be if there are no leaks).
Just use the same good quality silicon you intend to use to re do the seams. You may have to trim off any old excess silicon to give an even surface.
When I added the plastic angle strips to my tanks I lightly sand-papered the inside of the angle to roughen the surface for better adhesion.
You may also need to use a little masking tape to hold the angle in place whilst the silicon dries.
I have only seen the angle trim here in black or white (I used white) so it would be interesting to know if it is available in any other colour, perhaps brown to match any house hold furniture etc.
I bet you have a few people who read these forums very curious and interested with your project and I'm sure they all wish you the very best of results.
Please keep us all informed.

Well I have a dilemma with the tank. I don't have a job, and only have $120 cash. My mom won't lend me the money upfront to buy the tank, because she doesn't want to see me waste my money on something that has no guarantee.

So I've reached a stalemate! :angry:

I'm still looking for a big tank second hand, but it may not be this one. In which case I could have the history of the tank, and possibly see it full of water. Which would save me the job of resealing!

Your advice is invaluable, and who knows, maybe I can bargain with this lady and get this beastly tank! Thanks a bunch, and definately if I get to try it out I'll let everybody know how it goes. Thank you again Rudolf!

Sorry to hear about your dilemma with the tank. I know you will be very dissapointed however I'm sure that other opportunities will arise for you. In the long run it is always a great thing to have parents on your side when you are interested in a particular hobby.
Keep your chin up!