It's hard to tell what you should do from what you've said. Try posting some pictures, or filling out this troubleshooting form:

http://boards.cannabis.com/plant-pro...ing-forms.html

As for the tin pot... NO do not use it. The sides will very likely rust, and although I'm not 100% sure what rust would do to your plant, but I highly doubt it would be good. Iron levels would probably skyrocket, if not worse.