That looks like Staghorn algae. It's pretty easy IMO to get rid of.
How long do you run lighting daily? Do you have good circulation in the tank as I've found low flow throughout the tank seems to encourage it. What is your nitrate level? What ferts are you using? Are you using liquid carbon or CO2?
You can spot treat it with Hydrogen Peroxide 3%. Turn off your filters. Pull 1-3ml of Peroxide for every 1 gallon of tank water up in a syringe and slowly squirt the algae. Leave filters off 20 minutes. If you have a lot you need to treat you can do an area a day. Then run lighting 6 hours and increase circulation. I use nano pumps if I need to increase circulation in a tank.