I recently shocked my pool, but a couple days later I noticed a few areas on the sides of my pool and spa that were a bit yellow. I'm honestly not sure if it was there before the shock or not, but I'm guessing that it probably was, and that I just didn't notice it yet since it was fairly innocuous. It easily brushed off, so it seems clear that it was algae, but I'm unclear what the visual results of successful shocking are. In other words, after shocking, can the yellowish color from algae still remain until you physically brush it off, or should the shock have made the yellow color go away if it was successful even without brushing? I'm not clear if the yellow after the shock indicates that the shock was not strong enough, or simply that it needed to be brushed afterwards in order to fully disappear.
It's been a few days and the yellow hasn't returned, but I need to know if I should once again shock the pool. Note that the water has remained totally clear throughout the process, and I have only minimal Chlorine loss overnight (about .4 ppm drop), and 0 CC in my readings (using the Taylor K-2006 kit.)