That is BBA and Siamese algae eaters do eat it as stated above. I would clean out the filters and I would manually remove as much as possible. Remove the pebbles, wood and decorations with BBA and soak them in a 10:1 bleach to water solution for 24-48 hours. This should kill the BBA. Rinse well with hot water and let air dry over night to allow any remaning bleach to evaporate. You can then put the hardscape back in the tank.
If you decide against CO2 I would reduce feeding and light and clean the filters more often. Actually, this is generally good maintenance anyway.