hair like algae

[angelfish]

I have a three month old freshwater tropical tank (120 litres) with live plants. Recently some of the plants have grown this hair-like algae which you can pull off - but it just comes back. The water is fine in terms of nitrite levels etc and the fish look healthy. It doesn't look nice though - what can I do? I am worried that when we go away for a few days it will take over the tank!
Thanks.