If I am seeing this right- the purple stuff is coraline algae, it's good. You want it unless you hate the look of it. I believe it helps reduce nitrates and adds color to the rock!
I think the brown stuff is diatoms. If you give the water just above the brown stuff a little swish, does the brown stuff move around easily? Like, lift off the sand and float in the water column? Diatoms blooms happen because most sand has silicates in it. They eat the silicates. When the silicates are gone the diatoms disappear. While ugly to look at they will go away with time. Pwc
's where you siphon just above the sand will remove some, but they won't stop until the silicates are gone.