Cloudy water as in your avatar is a caused by a bacteria bloom. Sometimes the cleaning of all filters at once, or changing/over cleanning of the substraight can trigger a bacteria bloom, due to the removal of bacterial colonies that had settled on the filter media or substrate. If a great deal of the benificial bacteria is destroyed, the bacteria are either re-establishing themselves, or are feeding on the elavated levels of nutrients. In nutrient rich new water they can multiply at such a high rate that the water becomes cloudy in hours. Also you could keep the lights off for a few hours after the water change this sometimes helps. Don't clean both filters at the same time alternate cleannings to keep form destroying too much good bacteria at once.
I just read your post above. You should have filter floss in the filters but really don't need carbon. Weekly water changes of 50% and alternate cleanings of the filter media should sovle your problem.