As a former spa dealer who started out selling, delivering, and servicing hot tubs, I know that 99% of the time, cloudy water has one cause – insufficient and/or ineffective sanitizer.
Regarding ineffective sanitizer, if you are using chlorine (and that includes dichlor, most salt systems, and most mineral systems) your chlorine may be ineffective as its ability to kill and remove bacteria and other pathogens is dependent on the pH of your spa water. If your spa water pH is above 7.8, the chlorine is doing almost nothing to sanitize your spa water.
