I would recommend using excel as a carbon source as suggested above, you should be able to grow Anubias and crypt species very well even with med-high light.
If you want to reduce light intensity, you can add 1-2 strips of window screen placed between the lights and the surface of the water. This effectively reduces the light and the more layers of screen you add the less light passes through.
You also stated the lights stay on for 12 hours, for plants 6-8 hours may be enough.
The best substrate for growing plants would be ada Amazonia aquasoil. It is more expensive, however one small 3L bag should be more than enough. If you decide to use this, make sure you let the soil sit in a bucket with water for about 3-4 weeks changing the water every 3-4 days to leech out ammonia prior to adding to your tank.