Hi shub_31. I merged the thread you started this morning with this one. Instead of starting multiple threads about the same problem, it is better to just reply to this one and keep everything together. it gets confusing to help in multiple places at the same time.

Have you done all the things Ben suggested in his post above?

If you lost 10ppm of chlorine overnight, then you are fighting algae and need to continue to shock your pool up to 25 or so. Test as many times per day as you can and each time, add enough bleach to get back to 25ppm. There is no such thing as testing and adding bleach too often when you are fighting something in the water. Continue doing this until you can go from sundown one evening til within 2 hours of sunup the next morning without losing more than 1ppm of cl and also have no greater than 0.5ppm of CC.