It seems that when I shock my pool, it looks fresh and crisp. As the FC drops to normal levels, it crosses some threshold and loses it's crisp look. I'm guessing that line is .05 HOCI, because after my pool dropped below 10ppm FC, that's when I noticed it wasn't as crisp. The spreadsheet says I need 9ppm FC to get .05 HOCI. I'm going to push my chlorine back up to 9ppm and see what happens. What do you think? Could this be an algae problem still? I just brushed my pool, like I do every weekend. This time, there was some brown dust that would brush up in many places.