Understanding chlorine tests....

[ewkearns]

Concerning the chlorine bound to CYA:

1) I think it is safe to assume it doesn't show up as CC, since I often show 0.0 ppm,

2) does it show up in any other test?


Does the "total potential chlorine" (I made that up) have any possibility to act as overdosing chlorine?

 

[Patrick_B]

The test finds it regardless of Cya. If there is FC or CC there, it will indicate it. If you run FC often, and know your pool, it's safe to assume no CC. Check once in a while to be sure. If you run FC 3 or more times a week, check once for CC.

 

[ewkearns]

I guess, then, using the following table:

CYA (Stabilizer)	Minimum FC	Target FC	Shock FC
20*​	2​	3​	10​
30​	2​	4​	12​
40​	3​	5​	16​
50​	4​	6​	20​
60​	5​	7​	24​
70*​	5​	8​	28​
80*​	6​	9​	31​
90*​	7​	10​	35​
100*​	7​	12​	39 ​

What is the "target" number for chlorine? If we had 0.0 CYA, would it be (say) 2 ppm? What should it be? At a CYA of 100, does the target of 12ppm yield the same amount of chlorine ready to do battle with algae and other critters that was had at 0.0 CYA and "X" amount?

 

[jblizzle]

Target is about where you want to raise the FC to every day ... although it is really MOST important that the FC never drop below the Minimum. So you should target whatever you need to keep it above the minimum. A 2-3ppm FC daily loss is pretty normal.

With 0 CYA, the FC would be even lower than 2ppm. Check out this chart which shows the "active/effective" chlorine level as a function of FC and CYA:
https://www.troublefreepool.com/~richardfalk/pool/HOCl.htm

At 100ppm of CYA with a FC of 10ppm, the active chlorine level is 0.043
At 0ppm CYA to have the same active level, the FC would only need to be 0.1ppm ... which is impossible to maintain. So most public pools maintain a FC up around 2ppm with 0 CYA which has an active level 1.0. This many many times more harsh than the levels we recommend and this is why we always recommend some CYA in the pool.

 

[ewkearns]

Thanks....! Trying to convince my PB that Bleach was not sent from the gates of **** to consume all vinyl liners, I realized a lot of things I hadn't really wrapped my head around.... yet. This was, to me, the most troubling piece of the puzzle I didn't really have.....

 

[Charlie_R]

Your PB must not know or care that chlorine is chlorine, no matter the source.

If you stay within the guidelines on your FC, you won't have a problem with your vinyl liner.