Almost certainly, you have high-ish calcium and ended up precipitating calcium carbonate particles. So . . .

1. Use borax to raise your pH, and avoid the problem.
2. Get a K2006 so you can manage your pH/alkalinity/calcium levels properly. http://pool9.net/tk/
3. If your calcium is high because someone told you to add calcium, but you have an FG or vinyl pool, STOP adding calcium. There's no need for it. http://pool9.net/calcium/

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