Where does the chlorine go if my cc is zero?

[subedoo]

My cc has been zero for a week now after doing an initial spring clean up. I'm holding my fc at between 3 and 6 ppm with a cya of 40. Last night I tested my water about an hour after I added a jug of 6% (had a heavy rain yesterday). The fc was 6.5 and cc 0. This morning, my fc is 5.5 and cc is still 0.

Where does the chlorine go? If it gets used up shouldn't it show up as cc?

[CarlD]

My cc has been zero for a week now after doing an initial spring clean up. I'm holding my fc at between 3 and 6 ppm with a cya of 40. Last night I tested my water about an hour after I added a jug of 6% (had a heavy rain yesterday). The fc was 6.5 and cc 0. This morning, my fc is 5.5 and cc is still 0.

Where does the chlorine go? If it gets used up shouldn't it show up as cc?

Not necessarily. CCs only happen when the chlorine binds up something. For example, UV rays lower FC with no other effect. So does exposure to open air. Also, FC breaks down CC as well. If you FC is 10x your CC (I think that's the ratio), the CC will break down. So if your CC is below .65 and your FC is 6.5...VOILA! no cc.

[chem geek]

And ultimately the chlorine (hypochlorous acid) ends up as chloride ion which is part of salt (sodium chloride). Other end products include oxygen gas (breakdown from sunlight) and nitrogen gas (oxidation of ammonia) and carbon dioxide gas and water (oxidation of organics).

Richard