Fake out the overnight test?

[rodrigo]

Just a trivial question, which I'm asking out of curiousity.

Does the overnight chlorine drop test REALLY have to be done overnight? Can the test be faked out if you have an automatic cover?

I've never been UNDER my pool's cover (by design, of course), so I can't say for sure if it's 100% opaque. But it's a very heavy vinyl, darkish blue, and almost always has a layer of dirt covering the whole thing (cleaning it is my least favorite thing in the world). Avoiding direct sunlight is key to the process, right? Does a pool with such a cover meet this? If so, how many hours of being covered would constitute a valid test period?

Just thinkin' out loud here... :|

 

[MikeInTN]

Good question. If I had an automatic cover, I'd try testing at sunrise, at sunset, and at sunrise again and see what the difference in chlorine usage was between daytime and nighttime.

 

[chem geek]

Yes, you could do the test during the day if your cover is opaque to UV light. I know that my cover is mostly opaque, but some light does get through and I don't know how much is UV but suspect not that much since chlorine usage is low and seems to be independent of sunny vs. cloudy days. I'm at around 1 ppm FC loss per day, but the pool is open 1-2 hours pretty much every day though that doesn't seem to make a huge difference (I've sometimes measured 0.8 ppm FC per day, but that's about the lowest daily usage with pool temps at 86-90F).

As was noted by Mike, you could do a comparison test of chlorine loss between day and overnight, accounting for time between test measurements.