I have an in-ground pool (approx. 15,000 gallons). The water has been crystal clear since the beginning of June. One morning, I awoke to find it so cloudy that I could not see the bottom. The PH was low, so added PH and then clarifier.
The readings on PH seem to bounce all over. Today here are the readings:

Hardness 200
PH Between 7.5 and 7.8
Alkalinity 240
Cyanuric Acid 0

Where should I start?