If you tried to bleach your tub whiter but it came out looking like a murder scene, DON'T PANIC! You can fix it for about $1.50 and no elbow grease.
I recently moved into an apartment in Berkeley. It's a nice big place, but kind of a fixer-upper, with a fair amount of cleaning to do.
One of the problem areas was the bathtub: it looked a bit dingy, with vague yellow streaks down the sides. So I bought some bleach, rubbed it on thick, and let it sit for a couple of hours.
When I came back, my bathtub looked like a scene from a horror movie. Literally: rusty red-brown streaks all down the sides and bottom like dried bloodstains. Exactly how I imagine it would look if you murdered someone in there.
Naturally, I freaked out, turned on the shower, and started scrubbing- to no avail.
My next recourse, naturally, was the internet. After frantically googling search phrases like "bleach blood bathtub stains" and learning some interesting but ultimately unhelpful factoids regarding the reaction of urine and bleach, I struck gold at this somewhat obscure link. A miracle. You don't even have to scrub. So I thought I'd take some pictures and turn it into an Instructable, surfacing the link more readily for other desperate fools like me.
Hydrogen peroxide– ideally in a spray bottle.
OR Oxi Clean
OR Clorox 2
(also work, according to various internet testimonials. But the peroxide is cheaper and more ubiquitous.)
The Science (as I understand it– Chem geeks, please correct me)
Why the tub turned red: The bathtub is an old porcelain with a ferrous (iron) component. The chlorine element in a classic chlorine-based bleach oxidizes the iron from the porcelain. Oxidized iron is rust, hence the rusty red color.
Why the tub turns white again: Hydrogen peroxide, Oxi Clean, and Clorox 2 are all chlorine-free cleaning agents (also the reason why they're color-safe) which have oxygen as a base element. I'd originally thought that since the red stains were also oxygen-based, we were seeing simple dissolution. But as ancienthart points out, that should only have loosened the stains and caused them to run down the sides. Since the stains instead disappeared without having to be wiped away, ancienthart suggests that it might be because oxygen is a reducing agent with basic solutions– so the oxidized stains are actually changing their chemical composition– and in this case probably also releasing chlorine gas. Make sure your bathroom is well-ventilated; you don't want to breathe in too much chlorine gas!