any of the other answers are correct but if you still have stains it will be that you have left the problem too long in which case i suggest you get a new shower curtain and start from scratch but be careful not to leave bleach on for too long as this will eventually rot the curtain. watch for the mould starting to appear and deal with it immediately and you shouldn't have any more problems, i find the mould and mildew spray the best but check the lable for it's suitability for your curtain and yes it is a good idea to wash it in the machine once a month to get rid of any residues on the rest of the curtain anyway and in the summer hang it on the line, they are a bit of a pain but i hope i've helped .