Step One: Put on a face mask to protect yourself during the process. Black mold can be toxic and inhaling the spores will wreak havoc on your lungs. Long rubber gloves can be helpful too, especially if you plan on using bleach.
Step Two: Use a hairdryer to dry out the mold. Black mold thrives on a dark damp environment and the heat from the hairdryer will kill a lot of it. About five minutes will be enough time. Make sure you dry the entire tub, not just the area with visible black mold. If it is growing in one place, tiny spores can be attached all over the tub.
Step Three: Spray the entire tub with bleach or vinegar. Pour either substance into an empty Windex bottle or sprayer bottle. Do not dilute, you will need the full strength for this job. Bleach is more effective, but also a dangerous substance. Be sure not to get it on your skin or eyes! Vinegar is less poisonous and many people prefer it because of this. Either will kill the remaining black mold.
Step Four: Wait ten minutes. The bleach or vinegar needs time to act. Now scrub the entire tub with a stiff brush. This will remove the mold particles and drive the bleach and vinegar deep into the surface of the tub. Again, don’t forget the areas where the mold is not yet visible.
Step Five: Thoroughly rinse with hot water. Make sure that all of the mold, as well as the bleach or vinegar has washed down the drain. Use the blow dryer to completely dry the tub. Make sure that there is no moisture remaining by wiping down the surface with a towel.