My pool looks great, and all my test levels are great. However, the little glass "jar" that is connected to the backwash gets dark green fairly quickly. I backwashed a week ago, and just added CYA a few days ago, so I can't backwash again for a few days. Why does that little glass jar get green so quickly ? And do you backwash as soon as it does? (mine starts turning green after only a day or 2)