I usually leave the bark on with oak twigs.
Do you have any livestock yet? One of the things I uncovered while reading up for my tank was that lack of Nitrogen (ammonia or nitrates) can tip the balance in favour of the bacteria. I can't verify this but I did have plants growing for 2 weeks before I added fish and was adding micro nutrients (Flourish comprehensive) but no macro nutrients (NPK).
To be on the safe side I have ordered a new LED as well. The one I have been using is over 10 years old so there is no guarantee the spectrum is still the same as when it left the factory - and LED lights have come a long way in the last 10 years. The other reason for the new light is the old one is not dimmable and my tank is long (i.e. its a big light unit) but shallow, so it could just be intensity.