Small white platelets close to the backflow are most likely to be particles of scale released during the self-cleaning polarity reversal of the chlorination cell. If the deposit is evenly distributed over the pool floor then this is most likely due to hard water rain.  Proceed as follows: Treat using a flocculent, Check the operation of the swimming pool filter, ensure that the swimming pool water is correctly balanced (pH, TH, alkalinity). See the water balance  section.