First try running your lighting only 6 hours daily. Then remove the decorations, lay paper towels down in a sink, put the decorations on them and squirt them down with hydrogen peroxide. Use the peroxide wet paper towels to lay over the decorations and let sit for 20 minutes. Then just put them back in the tank, no rinsing needed. If it is a type of algae it will die off. If that doesn't work I don't know what to tell you.
You also need to put root tabs under any swords, crypts, or bulb plants and then get some Flourish Comprehensive and dose weekly after WC's. Your plants need some type of fertilization.