whats the best way to get rid of and/or prevent mold/mildew in my shower?

i have a tub/shower that a small line of black mold or mildew (i dont know the diff.) keeps building up. i used this cleaner with bleach which worked great but are there any other more environmentally friendly, non-hazardous ways to prevent or clean it? just re-state, i would no longer like to use bleach, ill say it again just because most people seemed to have missed it the first time.