Does the tank get hit with any light from a window? I'm just curious.
Many people add a bit of carbon, ChemiPure or Purigen after the cycle ends to help clear up the water. The common way to check if you need it is to do the bucket test. When you do a water change you put the bucket of fresh saltwater next to the bucket of removed tank water. If the tank water looks yellowed compared to the new water you'll be able to see it clearly, side-by-side. If it's close to the same clear blue color then chemical media won't be necessary, at least for color polishing. It only works with white buckets though.