Looks like a case of low cyanuric acid ??!!? Tri-chlor tabs being used and low cyanuric acid? Very Interesting!
Any chance your pool having an Automatic Water Level device and perhaps a leak somewhere?

If not, it's possible that your low cyanuric acid is allow the sun's uv rays to degradate the chlorine.
You can use a Salt Chlorine Generator, but as with very wise recommendations, you're better off upsizing the cell to the largest one you can afford. This should provide a higher chlorine output, longer warranty, and longer cell life.