As posted in another thread on algae, my pool water and pool were pristine, until I put the solar cover on and left it on. For some reason, there is now algae on the pool walls, although I have kept the cl level up to 5 or 6 since opening two weeks ago. Anyway, so now, with a cya of 40, I'm guessing I need to keep the CL up to about 15 to kill algae, right? For how long? The water is still clear, by the way, just green algae on the walls. So, I keep the CL up around 15 for some period of time? Now, how about swimming? The temp is coming close to 70, and those two wanting to swim and not being intimidated in the least by it being cold, will be begging to get in! Can they?