Is this normal

[Wild Duk]

I just installed a new SWG. At night after the pump shuts off, I test the FC and its around .5

I test in the morning after the pump comes on and the FC is around 3.......How does it go up overnight???

 

[duraleigh]

It doesn't, unless you have some other source of chlorine in the pool (floater, etc.)

What test (OTO, DPD, FAS/DPD) are you using? A testing error is the most likely suspect.

 

[JasonLion]

Is there any chance that the pump is programmed to run for a while in the middle of the night?