Re: Unexplained FC Consumption (updated title)
One possible theory I would like propose is the level of UV exposure as compared to previous years. Several times you have mentioned your FC loss in relation to last years losses. Looking at a historical UV chart for last year in Cleveland there where far fewer days of very high UV levels (35 days) compared to previous years (i.e. 2012 had 58 days and 2011 had 70 days). Could it be as simple as more intense sun exposure? Not sure if this would explain all of your losses but it could help account for some.
WOW - I never thought about that angle....I guess we need chemgeek to try and help us understand the details...I guess I would get another PPM per day, but not the wild swings I am seeing. But it COULD for sure have effects.
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Would the cover intensify the effect of the UV?
chemgeek posted this in another thread, so I don't think it intensifies...although I could be misunderstanding.
It depends on the clarity of the cover. If it's a very clear cover, it will let a significant amount of sunlight through, both visible and some infrared and some UV. Such covers do truly aid heating of the pool during the day. For an opaque cover, if it's white or reflective then there will be little heating of the water, but if it's a dark opaque cover then there will be some heat transfer for thin covers such as electric safety covers. For bubble-type covers, there won't be much sunlight absorption and heat transfer unless the top part of the cover is clear and only the bottom part touching the water is black or dark.
So in order of heating, it is the following:
Clear bubble-type cover -- passes through the most sunlight, retains heat well
Clear-on-top, dark-on-bottom, bubble-type cover -- dark bottom heats up from sunlight and passes heat to the water, retains heat well
Dark opaque thin cover -- dark cover absorbs heat and passes it to the water, but the thin cover doesn't retain as much heat
White or reflective bubble-type cover -- does not absorb heat but retains heat well
White or reflective thin cover -- does not absorb heat and the thin cover doesn't retain as much heat
The main trade-off is that the clear covers also pass through UV so while you get heating from sunlight passing through, you also get breakdown of chlorine.
With no cover at all, there is substantial absorption of sunlight which heats the pool where a white plaster pool with 4.5 foot average depth absorbs 60% of the sun's light energy and heats the pool at around 0.7ºF per hour with noontime sun. Competing with this is water evaporation where the same pool would lose about 5ºF if 1/4" of water evaporated. Evaporation depends not only on the water and air temperature (except for perfectly dry air), but also depends on the humidity and especially on wind at the pool water's surface. See the thread Water Absorption and Heating from Sunlight for more technical details.
