undulated trigger attacking power filter

[fugu]

i have an undulated trigger 5" in a species only 40 gallon tank (he is waiting for his 75 species only to cycle).
i recently added another power filter which sits inside the tank the filter has 4 suction cups and was attched very firmly to the glass. the trigger routinely charges at the filter and has twice dislodged it. any ideas as to why this animosity toward the filter?
thankyou in advance for any posts

 

[grouperhead]

undulate's are notoriously mean. my thought on this is he thinks the filter is trying to take over his "territory" since the other filter was in first he was fine with it, but know theres the new filter he hasnt seen everyday like the other one. this is pretty normal for an undulate to attack something like that in the tank. good luck with your fish and your new tank, bo

 

[diatom]

Fugu, I can't tell you about your powerhead but I can attest that my Picasso will bite me everytime I stick my hand into "his" tank as well just about anything esle I stick in there. The other fish he leaves alone... but me he likes to bite. Ah well I guess I prefer it that way.

 

[stormbind]

Diatom does it hurt when your trigger bites you?