Black/blue/Green Algae

For all my years of fish keeping, I have never had a black algae problem. And now in my 55 gallon there are starting to be good amounts of black algae on my fake plants, and on some rocks, even some dots here and there on the glass.

A 55 gallon is NOT an easy tank to empty all out and clean, it is messy and takes all day.

I'm wondering do any of you know a way to get rid of this algae without having to empty my entire tank? My tank isn't in the sunlight so that isn't what's causing it, and my water is crystal clear, everythind is in perfect order, so I don't really know what is causing it. It just started and I've had this tank for a long time now.

My Pleco doesn't eat that stuff.

Any help or advice will be greatly appreciated:)