I doubt a UV will help at all since you don't appear to have a bacterial bloom. Rather in one of the canister filters stick a bunch of polywool filter floss. Don't stick it in the HOB filters since the water will just bypass it. Fill a canister with mostly that and change it monthly. It will help clear the water up greatly.
Your other option is to get a diatom filter or you can get an AquaClear power-head and the micron filter attachment for it. Run it on a timer for maybe 3-4 hours a day and it should help clear the water.