If it still looks dirty it might need rinsing again and again.
Altro are in Letchworth, Herts.
They have a good tech dept, I have rung them a few times and they are very helpful, they even sent me some of their cleaning solution free (that was a while ago though).
They will send you a cleaning spec sheet, type of pads to use etc etc.
But dont go to the offices they dont have a shop as such, they only do post.
Regards
Murky