How did my CC "suddenly" disappear?

[woodyp]

Ok, this stumps me. Did the old water test this a.m. with TF100. Got as follows:

FC------2 I know 3 to 5 is the range
CC------2
PH------7.6
CYA-----40ish

So I go the pool calc and add in enough bleach just to raise FC to 10 for a test. An hour later I retested and came up with FC as 10 as expected, butttttttttttttt..................when i did the CC test again just for grins------------it was suddenly back to ZERO? Didn't even register! I know the shock level for my CYA is 16 and I came nowhere near close to that. What the???????? Will CC magically appear if you are below the recommended FC level for for CYA content? It sure magically disappeared in a hurry!

Any gurus wanna run an explanation by me on this?
Thanks in advance.

 

[Bama Rambler]

Possible testing error?

 

[JasonLion]

Low FC levels often lead to CC. It only takes a little FC for CC to form in the first place, but it takes rather more FC to break down the CC. So it is common to get CC when your FC level is too low. CC will be broken down any time the FC level is reasonable, and more quickly the higher your FC level.

CC comes in several different forms. Some break down very quickly, others more slowly. It looks like all of yours was the quick to break down kind. (Or maybe Bama Rambler is right.)

 

[woodyp]

That's one of the few tests I can do that I consider myself "idiot proof" on! I had no idea that CC had different "forms". I just figured "bad" CC was "bad" CC. So you're saying that it is not unreasonable for that much extra chlorine to erase that CC in such a short period of time? Even well below shock level? It almost makes me think I shouldn't even bother to check for CC until I know my FC is in the proper range. This Texas pool in full sunlight all day is eatin' chlorine straight from the jug it seems. I need to give it a bigger straw and jack up my levels above the CYA/chlorine chart. Instead of the recommended 3-5 range, I'm gonna try and keep 5 as my bottom number using the same level of CYA. Probably raise my "add up to level" to 8 since I'm losing at least 3 ppm daily. Thanks for the input guys.

 

[JasonLion]

Try raising your CYA level up to around 60. That should help reduce the amount of chlorine you are using daily.

 

[woodyp]

I'll give it a go on the CYA Jason, thanks.

 

[geekgranny]

I raised my CYA from 50 to 60 a couple of weeks ago when the temps and sun increased. This increases the top number in range so I target just a little above the top number with chlorine additions and it holds well; stays within range for two days, under normal bather load conditions. I don't have an SWG; rather "jug dump" bleach.

gg=alice

 

[woodyp]

I'm taking your advice too gg. Lesson just learned on adding CYA--------DO NOT sprinkle in front of a return! Experimented with half of what I added to bring the levels up by adding in front of return. Looks real nice sittin' on the bottom of the dang pool! Will this hurt anything, or do I need to jump in and stir things up? Tried to stir it with the pool pole skimmer with crappy results.

 

[Bama Rambler]

I'd vacuum it up if I were you. That way it can sit in the filter and not hurt anything. It is a mild acid so it could possibly harm the liner.

 

[woodyp]

Vacuumed as recommended! Thanks for the info Bama.