What about CLR? I know it works great on Calcium, lime and rust in the kitchen and bathroom. (if you have hard water, use it in your toilet tank/bowl. Let it sit overnight)

 

Found this thread and thanks for the advice. I have the same issue as the original poster. I have a 6 gallon split tank so I got a gallon of white vinegar for both sides.

after reading this thread again I am thinking of putting 2 gallons of white vinegar in both sides to use after I use soap and water any other suggestions?