The last 3-4 years, when I've opened my 40,000 gal. pool, it's taken approximately 60 lbs or so of granular shock to reach the proper chlorine stability level. I always check the alkalinity and ph first, so that they are in order, but then I just keep DUMPING the shock in ....
I've had the pool for 25 years, but this is just a recent occurrence. Any ideas??
