Good call, Dave. I should have mentioned that it looks like it'll take 3# of stabilizer, but to put half in first, wait 5 days, then test. It takes forever for CYA to dissolve. After the 5 days, test, and then re-evaluate how much you need to put in to get to 40 ppm. You want to do partial additions, mainly because once CYA is in your pool, it's a real bugger to get out.

However, even though your Cl is getting nuked by the sun, don't stop putting it in. I would do your Cl additions at sundown (or when your pool isn't getting direct sun) to maximize the time that your Cl will stay in the pool. Once the CYA starts helping out with the Cl, you should be able to keep some residual.

Michael