Dirk mentioned a "reverse OCLT" above as a way to determine if your SWCG is working. So, to do it-
As you are planning bring your FC up to about 6 this afternoon with bleach.
After dark test your FC using the 25 mL sample for 0.2 ppm accuracy.
Turn on your pump and SWCG, set teh SWCG to 100%
Run the pump and SWCG
all night long
Before sunrise test your FC using the 25 mL sample for 0.2 ppm accuracy.
If your SWCG is working the FC should go UP overnight. We may be able to calculate if it working properly if you tell exactly how long it ran at 100% and the FC rise over that period of time.