How do you intend to use tubes to light the tank when the mangroves will be above the water line? If you hang the tubes in a rack above the tank then the light will defuse too much in a wider space. I dont knw if you will need anything quite as fancy as metal halides but you will certainly need to look at something like the spot type lights that are used in hydroponics. Try looking outside of the aquatics hobby for lighting solutions, when something has the word "aquarium" tagged to it they seem to stick another 10% on the price for the sake of it.