Chlorine levels not going down


Well-known member
Apr 13, 2017
Little Elm Texas
For the past few weeks I have chlorine levels running around 10-12.
I keep turning down the % on the swg.
I now have it at 20%.
What is keeping my chlorine levels so high? It was not like this the past few years.
Test results today
FC 10
TA 65
PH 85- not sure why it spiked
CYA 65
TCH 450


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Lower water temperature and lower sun angle this time of year reduces daily chlorine loss.


Bronze Supporter
Mar 5, 2020
Melbourne, Australia
Pool Size
Salt Water Generator
SWG Type
Astral VX 7T
How long are you running your SWG per day? And what is the water temperature?

Once the UV load and water temperature are low, it just needs a few days of running the SWG on "summer settings" to get your FC up.

In winter, I don't have to add more than 0.5ppm with my SWG per day, less than 2 hours at 40%.

How are you measuring your pH? A drop test will read falsely high above FC 10. A pH meter reading would still be correct (I assume you have a pH meter to get a reading of 8.5?)

While producing more chlorine than you are using, your pH can rise. Once you consume more chlorine than you are producing per day, pH will move down again and reach normal levels (assuming you have no significant pH rise due to CO2 out-gassing with TA of 65) once FC is back to normal - that's when the chlorination cycle will be closed.

Let's say you started at FC 5 and pH 7.8. Chlorine production with your SWG to raise FC by 7ppm to reach 12ppm will bring pH to about 8.4. Chlorine breakdown by 7ppm will bring pH back down to 7.8 (calculated with Chem geek's PoolEquations spreadsheet).

So, pH can be higher than normal until the extra chlorine has been consumed.