I couldn't tell you based on what I know. But I will say that it def. sounds bacterial. The EM might work, but it might not. Even if you kill it however, you need to address why it (continuously) showed up.
Keep up with dosing and w/c or dial back on the lights if you cannot dose midweek. Running short on nutrients in a high tech set up can definitely cause issues really fast. Remember, its not the most abundant nutrient affecting plant growth, its the least abundant.
If your tank never gets a chance to "beat" the bacteria or algae over the long haul, each week its getting a chance to come back.