I did the ascorbic acid treatment about a month ago. While the chlorine was at zero, I had Polyquat-60 in. The chlorine was brought back up slowly, as the directions for the ascorbic acid treatment indicated. That was finished 2-3 weeks ago. Based on what I've read here, I'm pretty sure that the ascorbic acid and Polyquat-60 effects on the chlorine are long past.
The problem is that I can't get the chlorine to hold. For the past 2 weeks I've been losing 4-5 ppm per day, as opposed to the 1-2 ppm per day that is normal for my pool this time of year.
Seven days ago I decided that I must have given algae a chance to get started despite the Polyquat-60, so I started shocking. I've held the level over 16 ppm for seven days now with no change in the daily loss rate. Sorry, but I haven't checked for overnight loss as I've been low on reagent (should have more arriving from Duraleigh tomorrow), but there's no way that I can lose 5 ppm per day to the sun in February with a CYA of 50 ppm, is there?
I've just about decided that it must be mustard algae and am thinking of taking the shock level up to 30 ppm (as per the Pool Calculator). But before I did that I just wanted to see if there might be any other ideas about this. Perhaps something related to the ascorbic acid treatment?
Here are my current numbers:
No CC observed during this whole process