Looks similar to what I've been fighting. Mine is probably due to overfeeding or the lights getting left on too long each day. I don't know of any other method to get rid of it than frequent water changes. I currently do 70% water changes WEEKLY and I'm still fighting this. Usually once 70% of the water is out of the tank, we put a couple of buckets of clean water back in, then suction it out, then repeat that again until we feel like the algae has been washed out of the gravel. We also remove and wash separately any plants or decorations. It's a huge amount of work. Sorry!