Estimating FC demand due to extra sunlight hours


Bronze Supporter
Mar 27, 2019
I just had a large tree over my pool get some major trimming which is yielding approx 3 hours additional sunlight per day in the morning. These 3 hours are from 9-12 so it isn't going to be solar noon but still much more direct sunlight. If I used to have FC loss of 1-1.5 each day based on 5-6 hours of sunlight, should I expect a 50% increase in FC demand? I know the correct answer for me is just going to be to do the testing to find out the difference but I am wondering if anyone has done any prior study/analysis.

Not all sunlight hours are equal and with clear skies right now at about 10am, our UV index is only 4. Memphis gets sun angle at approx 76 degrees during July so I know the intensity would be higher than for someone up North. The temp of the pool immediately went up about 5 degrees the days right after the tree limbs were removed.

Anyway, I am likely just trying to over-analyze but would like some thoughts on the impact of FC demand based on different degrees of sunlight during the day and total hours during the day.


Bronze Supporter
I've discovered that my pool needs about 2 cups of 6% chlorine (2 ppm) on overcast and cloudy days, and 3 cups (3 ppm) on bright sunny days. The amount of sunlight really does affect chlorine usage. What I would suggest is test every day for a week or two and make note of how much sun the pool got. That should give you a good baseline for dosing the pool according to the weather.


Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
Brisbane, Australia.
I would test and adjust. But it’s important to keep on top of major change, particularly an upward trend. I would increase the daily dose as per test results but also add an addition dose at each test to maintain your target FC.