Different LC Strengths in 2-pack

[hightechburrito]

I bought a 2-pack of gallon containers of liquid chlorine from the HW store a few months ago. They're supposed to be 10% LC, but the first one acted more like 6% based on how much it raised my FC when adding to my hot tub. I started the second bottle today and added what should have raised the FC by 5ppm or so, but a test ~30 minutes after adding showed about 10ppm increase. So the second bottle was acting more like the 10% it's supposed to be.

I'm planning on doing a more controlled test later (test before, add a small amount, test after), but would it be that unusual for two bottles in the same carboard box (so the same date code) to vary by that much?

 

[HermanTX]

That is strange that 2 bottles in the same carton are significantly different. Heat does affect chlorine strength so if one side was more in the sun, that could be a reason. Best to do your tests again and determine if that is same results.
You can search the TFP site for a method to test chlorine strength directly (right from the bottle), but I remember it required very precise measurements to get a proper result.

 

[hightechburrito]

Second test today and it’s behaving like 6% like the first bottle. I’m certain that my test yesterday was correct (tested with FAS-DPD, DPD drops and a strip and they all agreed). So my guesses are:

1) I just put more LC in that I thought.
2) The bottle had been sitting for a few weeks and I didn’t shake it up at all. Does LC “settle” or anything.

I’ll accept that I put in more LC than I thought, but is #2 plausible at all? Does LC “settle” such that the top layer would be stronger?

 

[HermanTX]

Does LC “settle” such that the top layer would be stronger?

Not that I am aware of. I never shake mine so I have never really tested that.