ok
when I snorkel, I see zones of algae and then zones of coral. The high air exchange, shallow, warmer areas are dominated by algae.
Algae in coral tissues can't absorb massive nutrients like free algae can. The free algae is a sink because it can literally double in size in a week (in my tank, it can). It's a safety net like no other to remove excess nutrients that would otherwise kill a tank.
I use it because I feed excessively... There's no way to match the "food" content of the reef while maintaining a sub-measurement inorganic N & P content of the reef ... without algae.
With my scrubber, I feed
yes - 4 bananas today.
and my scrubber:
and my fish and corals eat constantly without N and P rising up from under the measurement thresholds..