Green Dusting of Algae of Rocks - Nutrients, Photo period or both?

[DeepBlueSomething]

I recently switched lights - from one black box to another on my 40G Breeder. Since the switch - approximately 3 weeks ago, I am noticing a persistent growth of algae on top of rocks. The algae is easily removed with brush...

I am working to reduce nutrients with regular W/Cs bi-weekly.

My question -
Is this a sign of too much nutrients
Too much light
Both

What is the best action to take?

 

[Brew12]

It could be a sign of too small a CuC.