Hi, Anna,

Mark's advice is solid.....I'd put in one quart of muriatic acid (pump running) and retest in a few hours or so. Be prepared to add another quart if pH is still 7.8 or more.

This evening, I would add 4 gallons of 6% Clorox. That'll shock your pool and clean up any developing organics.

I'd also put in 3lbs of CYA. Don't back wash for at least 4-5 days or until you test at least 30ppm.