Cost of calor gas heating northern ireland

Janjel

We have just moved into a rented property and have no idea about the calor gas heating costs. No site shows cost. We had half a green tank when we moved in and it seems to be comi g downquite quickly in a week. Any ideas on cost of full tank and what we need to do to reduce costs. We seem to have to keep turning it on, off again then on again just to get hot water?

Any help would be really appreciated

Thank you