Odd/Angry Tang Behaviour

[SmallFry]

I've had a kole tang for quite some time - over a year in fact, and up until now he's been the model of good behaviour, very chilled out, not really bothering anyone..

The last couple of days, however, he's been going nuts trying to kill his own reflection in the ends of the tank. I've put aluminium foil that has been screwed up over the ends to reflect the light back in but not create an image for him to attack, which seems to have worked - sort of..

He's still half heartedly having a go at the front glass occasionally and still has his barbs out all the time. Up until now I'd never even seen them properly. At no point has he attacked any of his tank mates - only his own reflection.

I'm worried because he seems to be exhausting himself and bruising himself up on the glass - in short he looks as rough as a badger's ass.. My question is, has anyone else experienced anything like this, and is it likely to be a continuing problem, or just a teenage tang temper tantrum?

Thanks in advance,
Robin.