Staghorn algae appear as thick grey hairs on the edges of leaf margins. They can be hard to remove by hand. They differ from BBA (Black brush algae) in that BBA has a finer texture and usually darker color.
They can be triggered by tank instabilities that cause plants to be stressed - such unstable CO2 levels or irregular fertilization or a spike in ammonia/organic waste levels such as skipping water changes in a tank that has previously been on a stricter water change schedule.
Staghorn algae is commonly found attached to the edges of slow growing plants.
Watch video on how to change water for planted tank.