I am still pretty new at this pool maintenace stuff and it seems like I have always had a high total and free chlorine levels my first 2 seasons, but when I just checked under the cover I was suprised to see 6 on my chlorine level. I know there is some argument whether there is such a thing as chlorine lock, but is it normal still to be registering choline after the whole winter (I have added nothing to the pool)?