You don't need to change your sand. The only reason to change sand is if it isn't filtering - because it is gummed up. To clear your water, you will need to put in sequestering agent - more is better than not enough, keep your ph at 7.0, raise your chlorine to shock levels according to the "best guess chart", run your filter 24/7 - backwash and brush, you can also put a skimmer sock on the skimmer basket to help catch small particles - if you still have sediment in the water you may want to vacuum to waste.