If you have scrubbed and cleaned repeatedly and it still doesn’t do the trick, you may need to replace the caulk in your shower or tub. Use a box-cutter to score the moldy caulk and then pull it out with your fingers or pry it out with a screwdriver. Prepare the area for caulking by putting tape on either side of the space that will be caulked. Leave about 1/4 inch space. Make sure to use silicone caulk meant for showers and bathrooms. Apply according to the manufacturer’s instructions.