Do I need a guide for snorkeling at Pigeon Island?

You are experienced with snorkeling or diving so don't need a guide. His presence, however, is invaluable for your safety. He can tell you about the best places to see live coral reefs and marine life. Also in case of emergency, he can provide you with the help. However, whether to hire a guide or not is totally up to you to decide because you know most about your skills and needs.