Sometimes it depends where the tank is situated,if the tank is near a window and gets plenty of light,it may become more prone to algae,
Excess nitrate may lead to algae etc,especiallly in the un-planted
My main tank has hardly any algae,yet the 2 10g in the kitchen have more direct sunlight and have more algae in them.
The only time to worry is if you have algae sucking cats,has these need the algae in the tank.