Hi Lucy
Use Viniger to remove and hard deposits from the tank. Give it a good scrub out tith hot water, then fill it with a strong salt solution. You can use bleach to clean the tank, but you need to rinse, rinse, rinse, rinse rinse rinse again, then rinse and rinse and rinse... get the idea. A strong salt soloution works just as well as bleach, and is much easier to remove from the tank.
Good luck with the new tank. What is going to go in it. Other than water and a substrate etc...