Elbow grease. It's from too infrequent cleaning.

I haven't encountered a pink mould/mold, but I suspect what kills off black mould could do the same for pink. Several simple options here: http://blackmold.awardspace.com/kill-remove-mold.html

Just cleaning with any of those posted in that link..I usually clean with vinegar and some baking soda or borax. That pink is a combination of humidity and shampoo/soap..No, it's not from too infrequent cleaning..it will show up in 2-3 days..I don't know anyone scrubbing the shower every day

You don't need to scrub every day, but you do need to wipe it dry or squeegee. And address the lack of proper ventilation. Pink slime mold is most often found in toilets though, where it IS due to not frequent enough brushing.

I squeegee after every shower, clean and spray regularly. The pink thing is a bacteria that will thrive in humid area and in a combination of soap/shampoo and water Here is a short summary of this http://www.huffingtonpost.com/2015/03/03/pink-slime-shower-gunk_n_6793586.html