I agree, looks like hair algae. As stated above the best method isn't just one, it's a combination of all those above. Water change, use RO
water (water purified through reverse osmosis), check levels, reduce feeding amounts and days, and cut the lights. If not a complete blackout, only keep lights on for a few hours maybe 2. But no light is better. More than likely it's excess nutrients due to too much feeding or phosphates in your water. It's pretty easy to vet rid of once you get on track. If your tank is near a window than it'll be a little more difficult.