Clownfish

[Treef]

I have a pair of clownfish and for a little more then a month they were sticking together pretty much the entire time. Recently however one has begun to chase the other to the top corners of the tank and wont let him out of that area. I use to see the aggressor charge or nip the other but it always seemed harmless because I didnt see any damage, but now it just chases it around the tank until it sticks to a corner, currently its right ontop of one of my powerheads and i'm afraid it might jump out of the tank if this continues. Could anyone explain whats going on? I read up on some of their behaviour and this seems more aggressive then normal.