From my experience with algae overgrowth, there's a simple cause and that's too much dissolved food (nutrients) in the tank water. Simply put, if you feed more than your fish and plants can use, then the conditions are right for algae.
I gradually reduced the amount I was feeding. I now feed my fish and plants a little, twice a week. Fish and plants are tiny and do best with minimal food.
By reducing the nutrients in the water, there's no food to sustain it, so algae shrinks to the point it's barely visible.
"Fear not my child, just change the tank water."