That is a mess, but I had a tank that was just all green algae, couldnt even see the rocks, at all! lol
Anyways, i would dose per the instructions exactly, chemiclean. get rid of that red slime algae so you can see whats going on underneath it all.
You can use api's marine version of algae killer. That will grt rid of some of the algae. Now, if there is any algae under all that like bryosis(sp?) then you will need to go about it differently.
And MOST IMPORTANT
you have to identify where it all came from and correct that behavior. This is all gonna just grow back if you dont, my suggestions are only to remove it for now and try to get a handle on things.
What kind of water do you use? RO
water, out of a machine, tap water? How often do you do water changes and how much water do you swap out? How often do you feed and what stock do you have in the tank?