I would like to start a 15-20g reef tank - few beginner questions help?! :( read please lol?

I could not agree with "Gren" more . I have had 2 saltwater tanks for over 15 years now (240 gal. & 125 gal.DO NOT even waste your money or time with any size tank smaller than 60 gal.Sure.the people at most fish stores will tell you otherwise ! Buy a book or go online to learn the basics .People get "fish fever" and buy the tank and whole set-up for $$$$$$ and after a short time sell it cheap. check recycler or craigs list Good Luck!