I made my way over with my kit for difficult tubs. This one was no piece of cake. A hard water problem had left a calcium deposit as thick as a Brooklyn accent after an all night bender. To make a long story short, 18% phosphoric solution sitting for 15 minutes and then 2 hours of elbow grease with a pumice stone left the tub looking like new. I'm a nontoxic kind of guy, but every so often a real doozy of a problem needs to meet the meaner stuff.