Didn't realize how much sun exposure changes chlorine demand hour to hour

Started by swamp_tyler · · 5 replies
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#1
been logging levels every few hours this week just to see the pattern and man, my chlorine tanks way faster between like noon and 4pm than any other time. same dose in the morning barely moves and by evening its still holding. makes sense once you think about the sun cooking it off but i didnt expect the swing to be that dramatic on a pool this size. anyone else actually track it hour by hour or is everyone just doing morning and evening checks and calling it good. kind of makes me want to dose later in the day instead of first thing but then it sits untreated all morning too. not sure theres a right answer here, just wasnt expecting the difference to be that big.

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#2
That midday burn off is real, but under the screen cage I barely see it, the mesh cuts enough UV that my swings are pretty tame by comparison. Never bothered tracking hour by hour, just check after my morning swim and again before dinner.

Honestly wouldn't chase the noon dip with a whole dosing schedule change, just run your FC a little higher in the morning so it's got room to fall through the afternoon and still be fine by evening.
#3
Morning and evening checks and calling it good is basically me, I dont have the patience to log every couple hours honestly. Chuck saying to just run FC higher in the morning so it has room to fall makes sense, thats kind of what happens naturally with mine anyway since the salt cell is putting out chlorine all day not just one big dose.

Since we went salt our swings arent as dramatic as what youre describing, no more midday reads that make me panic and want to shock the thing. I still see it dip some on the brutal sun days but nothing like tanking to zero by 4pm. Anyway if youre hand dosing liquid or tabs that sun burn off is gonna hit way harder than it does for us.
#4
No screen cage up here in Ohio so mine gets the full brunt of it, and I've noticed the same thing but never bothered charting it, just eyeball the water and my strips. On the real scorcher days, upper 80s and not a cloud around, I can dose in the morning and by the time I'm grilling dinner it's like I did nothing at all. Cloudy day same dose barely budges by evening. So the swing is less about the clock for me and more about whether the sun actually showed up that day.

No salt cell here so I don't get that slow drip Dana's talking about, mine's all or nothing whenever I pour it in. Wife thinks I'm nuts for checking the pool as much as I check the weather app but they're basically the same question at this point.
#5
Before I'd weigh in, swamp_tyler, are you running any stabilizer in that pool. Cyanuric acid is what actually slows the UV burn off, and if yours is low or at zero that midday tank you're seeing is going to be way more dramatic than it needs to be. I keep mine in the 30 to 50 range and even on the brutal Long Island August days my afternoon dip is noticeable but nowhere near what Bill is describing with his upper 80s scorchers.

Twenty five seasons of Memorial Day to Labor Day and I check morning and again after dinner, never felt the need to log hourly, but I did learn the CYA lesson the hard way maybe year four or five when I was chasing my tail all summer wondering why nothing held. Worth ruling that out before you redesign your whole dosing schedule around the sun.
#6
Tom bringing up CYA is a good call, swamp_tyler what does yours actually test at right now. Thats the piece id want to know before blaming the clock, since low stabilizer will make any dose look like it evaporated by afternoon regardless of what time you put it in. Mine sits around 40 and even on our worst August days im not seeing anything close to what you described tanking. Test strips wont give you a reliable read on that though, id actually get a proper kit reading before you draw conclusions either way.