I'm inclined to think your pH is low -- so go back to Walmart and get about 10 boxes of 20 Mule Team Borax + some distilled water. Go ahead and start adding borax, 1 box at a time, added slowly to the skimmer. BUT also use the distilled water to test your pH level.

And, check your pH test by adding a few grains of borax to the pH sample AFTER you've added the phenol red and taken a reading. The color should change to near purple.

Low pH is NOT good for vinyl liners, or for pool heaters, so get right on this.

I'm puzzled by the readings -- you've been using trichlor tabs all summer? And, you haven't had any algae or slime? In that case, I understand how your pH could be low, but I don't understand how you could have 0.0 cyanuric acid (CYA).