Are you using any fine filter media like polyester floss/fibre? These will help "polish" the water, but will need to be changed frequently as these clog quickly.
As for the spray bar, is this mounted above the water line, or low down near the sand? If it is mounted very low, this will just stir up the muck (which would normally be removed by vacuuming the sand).
What is the bioload? Are there fish like loaches that are constantly stirring up the sand? What are you feeding? Something that breaks up easily into little bits?
As an interim solution, you might consider "polishing" the water with a DE filter. This is a good option if you already have a convertible filter like a Magnum 350. I wouldn't run out and buy one since I don't think these are long term solutions. It would be best to get to root cause.
Lastly, how long has this been up. If it has been recently set up, give it some time to settle. Even with high turnover, it takes a lot of time for all of the water to pass through the filter.
Tim