Filter: Fluval 406 (383gph)
Powerhead: MaxiJet 900 (230gph)
Both of these put me at 613gph
I'm also already turning the CO2 on before the lights turn on, and vice versa. DC is pushing yellow, maybe changing the flow up a bit might help
Your flow doesn't seem that bad. I assumed they are directed where all your plants are swaying with no dead spots... even with carpet plant or low growing plants.
IME, I usually get BBA when I ran out of CO2, lots of light, and low flow.
I would spot treat the BBA with excel. Here is what I do, turn off all filters and power head for 15 minutes so there is no more water movement in the tank. Then take a springe or turkey blaster filled with 100% excel. Squirt the excel at the BBA location and leave it for about 10 minutes. After that, turn everything on. I usually treat it for two consecutive days. Then wait until 3-5 days, you'll see the BBA changed to pinkish color. That means they are dying.
Last, I would either increase your flow or optimize your current flow for maximum