I opened my pool 3 weeks ago and there was a little algae but the water was clear. I adjusted the PH, Alk, calcium and CYA was about 40. I cleaned up the pool and started slamming it. The day after opening the pool was crystal clear and sparkly but I was getting CC levels between 1.0 and 1.5 daily. I couldn't figure out what was causing the problem so I bought some filter cleaner that consisted of hydrochloric acid thinking maybe there was something nasty in the filter that needed to be cleaned out. That didn't change anything.
This morning when I tested the water I was still getting a cc reading of 1.5ppm and I figured I would never swim again. I had ordered all new reagents in March but I still had some DPD powder leftover that I had ordered last spring that I was still using. I store my reagents in a kitchen cabinet and the powder looked OK so I assumed it was fine. Wrong! I decided to test again using the new DPD powder and found that I have no combined chlorine. I feel like a fool for not thinking about trying the new DPD powder sooner and I'm pretty sure I will pass the OCLT tonight.
So, if your pool looks great and you are slamming forever you might want to try some new DPD powder. It will be much cheaper than running your filter 24/7 and buying huge amounts of bleach