Conch Shell Cleaning Without Bleach Allow the shells to dry completely before gently rubbing away all dirt and barnacles from the surface using sandpaper. Alternatively, apply a generous coat of toothpaste on the shells and let them sit for a few hours before cleaning out the dirt with a brush. For an even cleaner shell, try mixing 1 part lemon juice with 2 parts water and soaking the shell in this mixture for 30 minutes to an hour. Rinse well and dry before use. Conch Shell Cleaning With Bleach Use caution when cleaning conch shells with household bleach or other chemicals because they can damage the shell's soft inner tissue. If you choose to use bleach, dilute it first with an amount of water equal to the percentage strength listed on the packaging. So, if the container says 10 percent, then add 10 cups of water to the bottle. Let the shell soak in the bleach mixture for at least 20 minutes but no longer than 60 minutes. Then rinse the shell under running water for at least 30 minutes to remove any bleach residue. Conch Shell Cleaning With Vinegar Conch shells are made up of two main parts: the hard outer shell and the soft inner meat. To clean the shell, first soak it in a solution of one part vinegar to three parts water for 30 minutes to an hour. Rinse it thoroughly under running water and dry before using.