clownfish aggression... any way to reduce it?

[blueworm]

My new clown fish pair are being aggressive towards a smaller black clown fish which has been living in my tank for years.

I was just wondering if there is any tricks to reduce the aggression of the clownfish. My tank is not stocked at all, it has a black clown, bicolour blenny, pink spot goby.

Thanks please post anything that will help here.