You have way too many fish in your tank. Even with additional filtration, it will be hard to maintain good water quality with that number of fish unless you do large daily water changes. Forget about the live bacteria stuff. To lower nitrates, do a water change. Bio-wheels work well to provide surface area and oxygenated water to the beneficial bacteria. Additional filtration will help reduce the ammonia and nitrites in your tank, but will produce more nitrates.