Bubble cover problem

[dalehileman]

For 14 years we'd used a blue plastic bubble cover to keep our large below-ground warm in the summer. But for two seasons now in spite of our Mojave Desert hot weather the contents has been too cold to go swimming. Apparently it's because this last cover has proven porous, evaporation from its top surface keeping the water cold in spite of the usual hot weather.

Incidentally the evaporation leaves a whitish powder, sometimes tinged greenish or orangish, on the surface of the cover

(1) How can this happen, is it because (a) the plastic is defective in manufacture or (b) owing to our drought, constituents of the water have changed so it now attacks plastic, and

(2) The deposit proving not to be calcite, what do you suppose it could be

[dalehileman]

Hard to believe I'm the only SPH participant living in the desert with a bubble cover