Petition CSA means testing

I would like to see CSA payments means tested. My wife and I separated 2 years ago. I have never had a problem with paying for my children as they are both parents responsibility and play an active role in my children's lives, however my children live with their mother, which is usually the case in these situations. I have 3 children under 16 so the CSA were automatically taking 25% of my nett take home pay which equates to £400 a month. When we were living together, we were lucky to have £150 a month left after everything was paid and having my own bills and rent to pay now plus financial commitments in joint names, I am in serious difficulties. Surely a fairer way would be to means test CSA payments rather than someone in office making a 'best guest' as it currently is, or perhaps capping the amount someone should pay.