I have seen this with too strong of lights or with bad spectrum... they don't seem to want to reach out closer to the lights. When I saw this with too-much, it was 6x250W 10K XM over a standard 180G tank.. or about 1500 PAR 20 inches deep in the water and close to 3000 at the top. You do see this some with LEDs with ineffective white diodes that have bad/harmful peaks.
However, it is probably flow.