Best way to clean my home's water tanks?

Hi there! We live in a village and we store water in tanks on the roofs of our houses. The water is usually pumped into those tanks from a local well. However, recently after the war, we came and saw that the inside of the tanks are pretty dirty and need to be cleaned up. Someone suggested using chlorine after removing the water entirely then adding it back up. Is this safe? I believe chlorine is on the toxic list