Shock your pool tonight at dusk. Turn on the pump running it 24/7. Bring Cl up to 15-17ppm and retest again tomorrow AM. If you've lost more than about 1-2ppm, you've got some "bugs" in your pool that need killing.

Add enough Cl tomorrow AM to return Cl to the 15-17 level. Brush and vac frequently over the next 48 hours.

If you can test for CC, that would be helpful. Regardless, I think that's your issue. You should see improvement in the next 24-48 hours or so.