How old is the tank? Where did it crack? What are you heating it with?
Depending on where and how bad the crack is, you will most likely have to move quickly to get your snake a temporary house and get it out of that tank before it injures itself. At the very least, cover the crack with cardboard or something right now. Be very careful with tape....it's all too easy for a snake to get caught on it and get in a lot of trouble.