Out of town for a week, pool ran out of chlorine, came home to green lime soup. Added tablets to auto chlorinator and 5 gals of liquid chlorine as a shock and ran filter all night. Next day hand vacuumed on waste. Chlorine still seemed low, so added another 2.5 gals of liquid CL. Pool is starting to clear up, but is white cloudy. Have backwashed several times. Do you ever need to replace the sand in the filter? Friend said to add 2 cups of DE to skimmer, then backwash the next day. Will this help? Is my problem even filtration? Thanks