Here's a thought . My area of the country is very dry atm . So the sparrows are busy using my pool for a bird bath . Around the outside on the bottom of the pool were the solar blanket meets the sides and the top rail is alot of bird poop .

I mean alot , they really love this 24 ft birdbath .

I did take the solar cover off over the weekend and 3/4 went to live somewere else , were they could get a drink and bath .

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Donno if you problem is algae but it sure don't sound like the green stuff I used to get .

Does the cord on the temp meter get a slight green color ? Bet not , the sand dimples you talk about should have "hard" spots of green etc . Plus my stairs would get that "green" were they were screwed together etc .

gl
sprocket