Originally Posted by Gabe
What chemicals should I use? CLR isn't budging it.
If you're talking about a reddish brown stain where water drips out of the faucet and onto the tub, then you can use a fairly strong hydrochloric acid as well. The "enamel" on your bathtub is actually quite resistant to harsh chemicals like acids, alkalis and solvents, and hydrochloric acid shouldn't harm the enamel. (Check in an inconspicuous area to be sure, though, if you want.) Any hydrochloric acid based toilet bowl cleaner will dissolve that rust quickly, I'd expect.
However, don't let the acid get on any chrome plated bathtub drain flanges. Hydrochloric acid of toilet bowl cleaner strength will also eat chrome plating.
If you're talking about repairing rusting chips in the bathtub enamel, post again.