Well first of all before you even think about starting a saltwater tank you need to know your budget. How much money you have and how big of an income you have. The price to fresh water to salt, there is a astronomical difference in pricing of everything. From the tank, supplies, your not keeping corals it sounds like so lighting won't be much of an issue, and maintaining the tank. You need to have a steady income that will provide you with enough money to keep it running. I was in your shoes once. Been in freshwater for a while. Drooling over the cool fish and things in saltwater, and wanting to do one. After having everything planned out, I had to wait a year or more till I finally could effectively. You hear all those stories of tanks starting out bad and nothing good happens with them until countless amounts of money has been spent. I didn't want that to happen. So I waited till I could do it affectively. I'm young like you. I'm almost 16. It's hard running a tank inwhen you younger. Not much money I had. It was and is hard. So before thinking about the tank, figure out you budget first
