A breakout of cyanobacteria or dinoflagellates is not that uncommon for tanks at about 6 months of age. I had a real nasty outbreak of dino's as well
There are several things to consider here:
Nutrient export - likely nitrates and phosphates are the issues here, they are the limiting factor in algae growth. Step up water changes, feed less, start growing macro, and potentially look into GFO or BioPellets to aid in nutrient export
Flow - Increasing the flow in the tank may help keep them suspended where they can be removed by a filter sock (cleaned very often) or protein skimming
Lighting - Blackouts will help, you also want to look at the age of your bulbs if using T5 or MH (this was ultimately the cause for me) as bulbs age (and lower quality bulbs age faster) as these bulbs age, the light they put out shifts into the red spectrum, which fuels algae growth