how much light and how long is your photoperiod?
+1 this - also, do you have good stable CO2, and decent flow in your tank?
This looks like staghorn. In my experience with it, it usually happens when I have a CO2 problem, low flow from the filter being dirty, or just a dirty tank in general (yay laziness!)
Increasing flow, which also helps in co2 distribution, and cleaning the tank usually resolves the issue. If it's really going nuts on your plants, overdosing excel knocks it out in a hurry.