In my experience with citrus trees, shiny leaves are always an indicator of a problem. The shine is more than likely the result of bug excrement. Is the shine sort of sticky? If so I would look for signs of scale. Small brownish red spots that are attached to the leaves, almost always on the underside, but also on the stems. They tend to attack new growth viciously. If scale is the problem, they can be gently scrapped off the plants with your fingernail. I have yet to find a product that can totally kill them, I always remove them physically. Not sure if that is your problem, just offering my experience.