I don't think the sun burned it up...more likely, it was eaten up by the ammonia from all the junk the pool store had you put into the pool. Ammonia can cause quite a huge chlorine demand, but it's going to have to be overcome in order to get your pool back under control.
If the pH reading you got was a solid 7.0, then I would go ahead and add another pint of acid. If it was any lighter, then I would wait until the pH climbs a little bit--but then I'm pretty conservative when it comes to acid use. Brushing the walls daily would be a good thing to do, but I wouldn't try vacuuming yet, since you don't know what's at the bottom, and it will just waste water that you're trying to adjust. You might try scooping anything you can off of the bottom with a leaf net, though.
Janet
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