It has been my experience that water becomes cloudy when the concentration of one or more contaminants increase to a level which is sufficient to cause a bacterial bloom...no more, no less. In most cases, you will never know what precisely has occurred. It has also been my experience that your filtration system will probably not be able to remove the cloudiness. Just keep performing your routine water changes until this contaminant is consumed by the bacteria and/or sufficiently diluted and the cloudiness will disappear.