I'm having the exact problem as you, just seems to be a white cloudiness, it's really not too bad, but I don't like it as my tank was more clear. I got another HOB filter like you did. Didn't seem to help at all. Even water changes don't seem to help. I made a thread about it. If you figure out what's the deal, let me know.
http://www.aquariacentral.com/forums/showthread.php?p=585236#post585236
http://www.aquariacentral.com/forums/showthread.php?p=585236#post585236