I have a 27ft above ground pool with a vinyl liner. I am using a system called Sustain which is a calcium hyplchlorite based which i am having to supplement bleach to maintain a fc level. When i opened my pool about 2 weeks ago, i noticed some mustard algae in the bottom. So I purchased a yello free product that is activated by shock from my local store. I did have some mustard algae last summer that I had to treat. So i dosed my pool with 13lbs of shock over a period of couple days and by end day my FC would be 0. so i found your site and purchase 13 gals of bleach. Over last wkend I added the bleach trying to maintain a high shock level. Still no luck holding chlorine. I have tried the overnight test with just test strips. Last night to the best of my knowlege i did loss a small amount of chlorine. But it also rained here during the night. Had my Water tested today at pool store around 11;30a.m. Here are the results:
FC 2.9 - but had justed added about 1/2 gal bleach 1 hour prior
Water is crystal clear and has been since i treated it for mustard algea and shocked it
Went out to test water with strip at 2:00pm and the FC was 0
I seem to lose the most during the day with sunlight.
Im at a loss with what is going on. My pool store has no idea. We did test for phosphates but don't think there was enough in water worth treating. Also, Ive purchased the strips to test for ammonia. The results read maybe .25ppm. This was before I added my 13gallons of bleach. Retested, hard to tell but think it is 0ppm. Please help.