i think you can only have one element, the other one is like a backup i guess. i have a twin, and my element is fire. but i am really good in water too because that is his element. dont let people tell you it is because of your birth sign, and that determines element, because that is a lie. you should really try messing around with both elements and really find one you are comfortable and fascinated the most with. go swimming often, really have fun and feel the water and how it moves. go to a bonfire, or have a fire in your house and use your imagination. try to manipulate both of them. the one you feel most joyful or comfortable in or around is probably your element.