I too know this is an old thread but just had to chime in....
We recently moved our Niger from a 90 gallon to a 300. I thought I was going to be a hero. With all of that new swim space, I was certain I was about to create the happiest fish in the world.
Instead, the trigger has adopted a powerhead. He spends all day every day swimming around the powerhead over and over and over.
He will stop to eat, he will even play with the nori clip, but he always returns to the powerhead.
In the 90, he used to make runs up and down the length of the tank.
Sigh. Fish are odd!