I have been perplexed as to why I have high chlorine level (> 5 ppm) in my pool when I have not added any chlorine is over 6 weeks. Its probably been more like 8 weeks now.

I have a 10,000 gallon gunite pool, the CYA is at about 100 ppm. PH is about 7.4 - 7.5. Alkalinity is about 190. The water is crystal clear with no algae whatsoever.

I have tested with a OTO and its about 5ppm. I tested with a DPD and its almost 0 ppm. Leslies Pools has tested several times and they say its above 5ppm as well. I am not sure what they use (DPD or OTO) but I believe it is DPD.

Am I getting false readings using OTO? I tested on tap watter and the reading is 0 ppm using OTO.

Thanks in advance!