There is a very short break-in period after plastering a pool (2-4 days perhaps) where you have to be careful about adding chlorine. But after that, it should be no problem. Often times people are warned about the use of chlorine when in reality it's not the chlorine itself, but the amount used based on the pool's current CYA level. If you look at the "Chlorine/CYA Chart" link below in my sig, you'll see the proper FC level based on your current CYA for both Non and SWG pools. That is KEY, not only for proper sanitation, but to ensure safe, quality use of chlorine for the pool and swimmers. I hope this helps. If you have more questions, please feel free to checkout the ABCs of Water Chemistry located at our Pool School page (link also below).