Sounds like you have very cold water or you have alot of moisture in your bathroom, a couple of things that I can think of is make sure your flapper ball is not leaking by and causing the toilet to fill with cold water all the time , another thing you can so is try to get the humidity out of the bathroom by putting a exhaust fan in your bathroom . The next thing is you can buy a insulator kit that goes in the inside of the toilet tank that prevents the tank from condensating, or you can have a mixing valve put in witch mixes hot water with the cold water preventing the water problem.By the way its nice to know there is another person named toby and not a dog which I hear all the time!!!!