Something I've never seen before

The back side of my tank is painted black, so I never spend time to clean it.

I started to notice the different types of algae that grows on it.
Can it be the different type of lights I have?
I've got 5 x T8 lights in white blue snow red white again.
My tank is 600mm deep where the top 150mm is greenish algae and bottom is brown.

see attached picture what it looks like, it's a first time in my 25years of tanks

My lights were on for 10 hours a day but shorten it to 8.5 since algae began to become a problem.

Let me know if someone seen this before.

 

The picture turned for some reason it looks if it's on the bottom but the left side is top water surface

 

I have seen slight GDA on the back glass of my tank like this, but only the lower half. So I would say lights and reflectors . With reflectors , they all are not perfectly adjusted to shine at the same height , if you know what im trying to say .