For the fire I would suggest using several bulb lights (maybe 1 red, 1 orange, 1 yellow, each with a shorter distance than the one before). If you are animating, I'd apply the Jump behaivior so the firelight "dances". I'd place the lights slightly above and in front of your fire. For the fish tank, are you using caustics? Are you sure that Light through Transparancy is on in the Render room? Holly