Red Slime?
 

I am fairly new to salt water and have recently taken over a tank. I have some mushrooms and a few frags of coral in it that seem to be doing ok. I've noticed a redish purple growth forming on the rocks and sand. Could this be red slime that I should treat for or is it something else that I should be concerned about? Any input would be greatly appreciated.

looks like a bit of slime on the sand but its hard to tell from your pictures.
Rock looks okay I think.
Keep an eye on it it will get worse on the sand if it is slime and there will be less of it when the lights are off.