Chlorine won't come up...and other questions

[jblizzle]

Chlorine does not evaporate. The sun just breaks it down and it out gases, I am sure somewhere in a chem geek post there is an explanation.

Only the pH is affected at high FC levels.

 

[Azgirl71]

Thanks Lisa. ...and congrats to you also...I read every entry of your recent thread and learned a ton about the SLAM process.

YOU definitely know what you're doing!

Thanks you. Glad it helped you.

- - - Updated - - -

Good morning forum!

My pool passed another OCLT!
8pm: Fc = 20. Cc= .5
7:30am: Fc= 19.5. Cc= 0

Two questions:
- how does chlorine drift back down to more normal levels? (I'd be happy to hear the science behind it, if anyone knows)
- which tf-100 tests are effective at this chlorine level? (E.g. pH is skewed high when FC > 10)

The sun will bring the FC down with time. Congrats on passing! I assume pool is crystal clear too? After your FC drifts below 10 then you can do a full set of tests. I would not run a full set until then.

 

[chem geek]

- how does chlorine drift back down to more normal levels? (I'd be happy to hear the science behind it, if anyone knows)

The chemistry of chlorine consumption is described in this technical post, but for outdoor pools exposed to sunlight in low bather-load pools (such as most residential pools), the ultraviolet rays in sunlight split apart chlorine (hypochlorous acid and hypochlorite ion). This actually results in very powerful but short-lived oxidizers called hydroxyl radicals and is part of the reason why outdoor pools are easier to maintain with chlorine alone compared to indoor pools. Through a series of chemical reactions the end result is mostly oxygen gas and chloride ion (i.e. salt).

So in short the sun deactivates the chlorine back to salt.

If there is no sunlight, the chlorine still drops but more slowly. How slowly depends on what there is for chlorine to react with in the pool such as bather waste, blown-in organics (leaves, pollen. etc.) or a pool cover. There is also some very slow outgassing of chlorine but unless the water is hot with a lot of aeration (as with spas) the amount of outgassing is quite small.

 

[AChristie76]

Whoa! Guess I asked for that!
Thank you Richard.