i agree with Manoj. i would start with a large water change. if you reduce lighting, make certain you have media in there to catch the bacteria as it dies off, otherwise you are adding more waste to the water column.
you might already know this, but never use the stuff called "Red Slime Remover", as the Cyno is a bacteria, and that medication will destroy not only that bacteria but other beneficial ones as well. that will result in a re-cycle of the tank.