This is staghorn. I know it well, notice my sig line.
Ranges from dark grey to almost white, but with a hint of green if you look close. Longer than BBA, fatter strands when mature, and with a characteristic branching reminiscent of a stag's antlers - thus the name.
Never saw it at all in many, many years until it was imported on a new plant. Since then, I've had many massive battles with it. Now it apparently lays dormant in all my tanks, as it will rapidly make a reappearance should conditions favor it.
It loves high light. Even if the light isn't quite bright enough to induce it alone, it may still appear if there's strong flow across leaves. So it typically appears near the top of the tank, in a strong current. It may also appear elsewhere if leaves are covered with other algae, or weakened for any reason; though it won't grow as fast.
It will grow in CO2 levels from 0 to 60ppm, regardless of stability (or lack thereof). Even in the concentrated output from a power diffuser, the CO2 is no impediment; it simply enjoys the flow. No other nutrient parameter has any significant effect. Only limiting light and flow, plus keeping plants in peak health, prevents it.