A few weeks ago, I came home from a trip to a pool full of algae. I slammed it according to the TFP method, which seemed to work. However, about a week ago, the algae came back. I slammed it again, this time being much more careful and frequent with my chlorine measurements. Three nights ago, it passed to the overnight free chlorine loss test, the water was clear and there was no measurable combined chlorine. This morning, there was algae on the steps and some of the sides. I tested the water, and the chlorine hadn't even dropped to its target range from the slamming. Here were the numbers from the test:
Calcium Hardness: 210
Total Alkalinity: 90
Free Chlorine: 11.5
Combined Chlorine: 0.0
Water Temperature: 87.3 degrees
Can anyone venture a guess as to how the algae is forming? Could it be mustard algae, or some other resistant species? If so, how do I determine what kind of algae is it?