Every time I try to breakpoint shock one of the pools I run (a 27,000 gal therapy pool), it seems the combined chlorine goes up not down after I shock it! This is the process I use to shock the pool:
1. Backwash the filters
2. use powdered Pulsar shock adding enough to bring the free chlorine up 15 to 20 times the combined chlorine reading at close
3. backwash filters again in the morning before opening.
4. bring chlorine into legal range using sodium thiosulfate
Every time I have done this, the combined chlorine goes up in the days after I shock not down! Is there something I am not doing properly?