How to clean brown stuff that keeps getting on shower?

I'm not sure what the brown stuff is - maybe from hard water? Try this:

Fill a spray bottle with a 50/50 solution of Dawn dish soap and vinegar. Spray it on the stains and let it work. If they are tougher stains, you may have to scrub with a plastic scrubbie!

domestos.

Brown stuff? Could it be rust?

Pink,Orange,Reddish, Brownish colored scum---a type of water-borne bacteria, Serratia marcescens. The discoloration comes from a biofilm—that is, a bacterial colony—of Serratia marcescens. The airborne bacterial species thrives in moist environments like showers, where it feeds on mineral deposits in soap scum and fatty deposits in soap and shampoo residue. It can cause various ailments (e.g. urinary tract or bladder infections) if it enters the body through the eyes or open wounds. The severity and variety of these ailments increases in individuals with compromised immune systems. REMOVAL--Make paste of Dawn dish soap and baking soda using stiff clean/new toilet bowl brush scrub all areas then add some white vinegar(lots of fizzing) then scrub some more let sit 10 minutes or so rescrub then rinse with hottest water possible boiling is good. Need to put straight bleach on it after to kill it & to remove discoloration. Then let it sit another 10 minutes then rinse with hottest water possible.

Try CLR or krud kutter

I lived in an apt and there was a lot of iron in the water the shower turned brown. I would use VIM and it cleaned it very nicely.

If it is a growth, use straight vinegar on the whole area after you get it clean. Bleach is good, but vinegar is one of the best and handiest (everyone has vinegar) and cheapest things that is a great antibacterial and antifungal agent available anywhere. It kills almost all bacteria and fungal spores on contact. Leave it on and let it dry for the vinegar to do its work the best.

You can try this homemade cleaner also: https://www.onegoodthingbyjillee.com/how-to-make-powerful-homemade-shower-cleaner/