1. It is never a good idea to add shells from the beach into your aquarium. Introducing shells raw from the beach can add harmful bacteria and potentially new creatures to the aquarium.
2. You should be sure to rinse out all of the materials you are going to be placing in the aquarium with water. Do not use soap or detergents, soap can cause toxic results for the fish in your aquarium. Just rinse the equipment with distilled water.
3. Pay close attention to your fish's PH needs and augment your aquarium as necessary to accommodate the new fish you are adding to your aquarium.