Lots of algae, 0.5 CC

[aylad]

why didn't the level go up when I had algae.

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CC (combined chloramines) are formed when the chlorine is fighting something, like algae, in the water. They are eliminated by chlorine that finishes the job, and are also eliminated by burning off via sunlight. I've had algae blooms, bad ones that happened while my pump was out of commission, in my pool before and still had 0 CC, which is why I don't consider it a reliable sign of algae growth.