I don't know about filefish. But I do know that if you have a Aptisia eating Copperband, many of the Aptisia would go into hiding.
Once the Copperband is removed, the pests would appear again.
In short, you have to keep the Copperband in the tank.
I think the same applies to filefish.
The Aptisia would hide deep in the cracks that the fishes can't reach.
That's my personal experience.
Cheers,
Yt
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