Consider having your pool water tested for phosphates. I was having the same problem last year and discovered my phosphates were very high. It took some work to get rid of them, but whereas last year I was running at 80% with very little production, this year I am running at about 20%.

Also, slightly loosen the union at the downstream side of the cell and collect the water while the cell is generating. Test that water and see what the Cl tests.