Crazy AA folks here (my kind of people)
You will have to trim it as the fronds will continue to grow upward. Remove it from the tank, hang it upside down and snip snip with scissors.
Several years ago I actually filled a 20L wall to wall 6" deep with this moss under a single T-8, no ferts, no CO2, no clue. Had no idea what I was doing but this stuff just grew.
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