Moderator note- moved from this post. Can't keep the chlorine in - SLAMming in Canada!!
I am having a similar problem, for the first time in 7 years, I cannot keep FC. All the other readings are fine, except phosphates were high. I dod the PhosFree treatment, totally replaced DE. I have added 6 lb. of stabilizer, and multiple gallons of 12.5% sodium hypochlorite shock. It still reads zero FC! The pool is sparkling clear, no algae, no cloudiness. I have also been running my SWG at 50-80% output with no increase in FC. What am I doing wrong?