Okay, the cell tested OK at Leslie's. I bought it in May of 2015, so it should still be good. The generator ran fine all day yesterday, indicated salt level 2800. This morning the salt level indicated 2600, check salt and inspect cell both flashing, generator running. I'd received my Taylor salt level test kit. The salt tested to 5000. Wow! This test is a simple titration, with a possible error of 200 ppm, according to the directions, which say 1 drop of silver nitrate regeant = 200 ppm. I did two years of a chem major in college, so I've done lots of titrations.
pH is about 7.6 CyA is about 50.
When I opened the pool the control box indicated about 2600 ppm, so per the pool calculator I added about 120 lbs of salt, to make up for losses in backwashing, etc. And then the troubles described in my first email commenced. Pool Cl level is perhaps 1 ppm. I was able to loosen the union for the cell and measure a dribble while the generator was running, that measured about 3 ppm. The nearby Leslie's has an electronic salt measure device, I'll take a water sample in tomorrow morning when they aren't busy and see what they measure. I imagine that agreement within 10 or 15 percent would be acceptable. If salt level is truly that high I'll have to drain 25 - 30 percent of pool water.
Perhaps I need a new control board. Any thoughts out there?