Testing chlorine when the pump is not running

[Phillbo]

Does not answer your question but I've always done my test at the end of a pump run. I feel it gives me a better idea of what chlorine levels are being produced by my SWCG.

[famousdavis]

Actually, during this time when I'm still learning about my pool and SWCG, I have been testing twice a day, to find out whether I'm getting a net gain/loss in chlorine based upon the current SWCG setting, and also to see how much chlorine I lose overnight. I'll probably continue doing this for another few weeks, at which time I'll relax a bit. It takes time to know how much chlorine gets used based upon bather load and weather conditions, but I've learned a lot over the last few weeks. I still think I have more to learn, though.

[BigDave]

Is it at all possible that one of your swimmers made a "warm spot" in the still water?

[famousdavis]

BigDave: Nope. Among my wife and daughters, that isn't possible. And my youngest son likes peeing in the grass. ;-)

[BigDave]

Perhaps some other localized contaminant, lotion, perfume, hair product? My point is FC is consumed and CC is created when the chlorine does it's job.

[famousdavis]

Well, I could try testing the FC/CC levels again tomorrow morning, just before the pump turns on, to see if the FC level is lower and CC level is higher than it usually is. If that's the case, I'd rule out the theory that it was a one-time, localized contaminant and I'd favor some other pool chemistry is at work when the water is still. But if the FC/CC levels are the same (or nearly so) as when I take a reading with the water moving through the pump and filter, then the theory that it just happened to be some localized occurrence would seem to be more likely.

[BigDave]

Yep, perhaps (since you're experimenting) sample and test several locations and depths.
BTW you pool is beautiful - I'm so jealous.