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 take out any carbon filters in the aquarium when you are medicating your fish. The carbon in the filter will remove the medicine from the water, so it is best to remove it all together.
3. It is not advisable to leave your aquarium lights on at all times for the aquarium. You should keep the lights on for 8-12 hour periods at a time. If you want to keep the tank lights on when you arrive home, simply get a timer for the lights so your fish stay on a schedule.