diatoms

Right now the dry rock in my cycling tank has a bloom of diatoms, as expected. But after all of the nutrients it eats is gone, they should die off, and the cycle should be done or close to done. I was wondering when the diatoms die off, does the rock look any different? I heard some people say...

I am curious to to what type of algae this is, and what to do if anything about it. The pictures do not visualize it as well as seeing it in person. L I am referring to the dark green spots on the rocks. It is slimy, and Not easily removed off rocks. I have noticed that one rock is harboring...