Juwel trigon 190

A while back I went from a 120 litre tropical tank to a juwel trigon 190. Only reason I got the trigon was that it fitted perfect where I planned to put it to make room for the Rio 400 later on which I now have and setting up as a marine tank. The only problem I have with the trigon is I'm never 100% happy with the water clarity. It always seems to have a slight haze to it and sometimes Its even difficult to see the rear of the tank where the filter box sits. I've tried messing about with the filter media (ie putting the poly pad futher down as I thought it should be nearer the bottom to give the water leaving the chamber a final polish before going back into the tank. I also tried running it for a week without the poly pad all together as its always clogging up and though this would be hindering the amount of water flow) but everything I've tried dosnt really make much difference. Apart from the obvious water changes and using filter aid I'm starting to think the only thing left to do is bite the bullet and get an external filter for it which I did'nt really want to do.

Happy to try other suggestions before I think of doing this if anybody has any