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I don't leave the cover open at all (30 seconds top) after I use the tub then add the dichlor. I do leave it open when I'm shocking for 30 minutes or so.
Doing so will cause chlorine gas to build up under the cover. It creeps into the cover and breaks down the vapor barrier. This is not visible damage, and you don't know it's making your cover absorb water until the thing is so heavy you can hardly lift it. QuoteLeave the cover open for at least ten minutes after adding dichlor. Is that needed when you add the small amount after a soak (1tsp per person)?? I understand it should be open after shocking for 20-30 min.
Leave the cover open for at least ten minutes after adding dichlor.