The smaller leaved floating plant looks like a species of Salvinia. In the past I have had what was sold as S. natans but looked more like S. auriculata, and on another occasion S. minima, but neither of mine looked quite the same as the one in your photo.
I found that mine went brown when water dripped on it from inside the hood, them the tank lights shone on the wet leaves. It was always worse in hot weather. Eventually it all died and I replaced it with water sprite.
Right on, this is what I was trying to remember yesterday. And xxtarajean, try carefully pulling the Salvinia apart; they should lie flat on the surface in a sort of chain.