Well, last night I performed a thorough cleaning, while siphoning off the pieces during a water change. The tank looked much better afterward.
I had to get up early for work this morning, and came into my living room about 15 minutes before the lights were scheduled to come on... and they were already on! I looked at the timer, and there was an additional cycle start timed for Midnight. Since my CO2 solenoid is plugged into a different timer to get started before the lights come on, I've been adding another 7 hours of light with no CO2 for the last few weeks. I'm guessing that explains my outbreak. While I thought the lights had been reduced to 8 hours, they were really only reduced to 15 hours (7 with no CO2). Sounds like a recipe for algae!
But really, since I'm still cycling this tank, I'm just trying to hold it at bay until the cycle ends, and I stock with algae eaters and start a dosing regime (I'll actually start dosing once the dry ferts arrive from Rex Grigg). As I said above, my only real tactic at this point is patience.
Ammonia still at 2ppm... 0 nitrites/0 nitrates.