Mischievous YWG or is something wrong?

[FishyFishy!]

I think that it would suggest that he is being chased up there by something/someone. You should try adding a pistol shimp in there to see if that might help. They can gang up and create a nice burrow.

I had a few YWG's without pistols, and they all perrished in the same way. It is strange behavior, but maybe thats just how they are when not accompanied by other YWG's or pistols. Can anyone else chime in here?

I would also use some egg crate and seal up that gap into the filter compartment.