Why are the discus fighting in this video?

[ujwaldignified]

I can see that there is a couple trying to pair up and the others are intervening. Please clarify and correct.
Thank u.
http://in.youtube.com/watch?v=lZQf4ZeNQ7Y&feature=related

[Patr1ck]

Did you change anything in your tank within a couple days prior to the fighting? One of my smaller ones was chasing around the big dominant one just like that after I added chemipure to the filter. The other fish seemed a little on the skittish side as well. I quickly removed the chemipure and did some water changes, which restored order to the tank. I dont know what changed in the water but the chemipure definetely changed my water chemistry. If I left it in there they may have adjusted, but I didnt want to wait and find out.:)

P

[William Palumbo]

You are right. Those Discus are becoming sexually mature and trying to pair up. That is when you will usually see more than average fighting...Bill