I've been fighting the past few weeks with my pool.
To keep the story short, I'll focus this one thread on a specific question related to FC and the amount of 12.5% liquid chlorine required to raise my above ground pool to Shock level.
My pool is roughly 7600 gallons or so (18ft above ground vinyl). According to the poolcac, adding 8oz of 12.5% liquid bleach is enough to raise the FC by 1. Yesterday my FC was 0.5, and my shock level is 16. The pool calc shows that 128 fl oz of 12.5% should raise the FC by 16 in 7500-8000 gallons.
So, I poured in 128 fl oz. A few hours later my FC was at 25, way above the expected 16. This happened to me last week as well one time. How can the FC raise so much in a known amount of water. The dilution is a known value based on the gallons in my pool. What else would have a huge effect on my FC level that instead of raising by roughly 16 I raised it by 25?