Hi Lgstacey,
The best solution is to launder the shower curtain and liner after every turnover. Well, maybe not the one-nighters but after every stay of three days or more. Do them in the washing machine and you can rehang them while they are still damp so they’ll only need a short time in the dryer or on the line.
I find it’s best to have spares too, just in case. I use white and so it’s essential that I have spares in case of someone dyeing their hair or something equally stainy. Although whatever colour or pattern, I’d still have spares in case the one in use gets torn or damaged in some way.
If you have a shared place and the bathroom is always in use, I would launder them every week.