So, do it a second time.
Do the vinegar. Let it sit for 3 ~ 4 days. Rinse, repeat. At only $2.50 a gallon, it's the cheapest thing going.
Or, pick up a gallon of swimming pool acid at the local Home Depot, Lowes, etc. Fill the tank 1/2 full with water first, add the gallon of acid, top...