It possible to be losing FC to organics even if testing is showing less than .5 CC. My CYA is 50-60 But I seem to be losing a lot of FC. I added bleach to get it up to 7, yesterday just before sundown. (although I didn't do a drop test to confirm after adding the bleach. I do know it jumped up to 5+ afterwards based on the basic test)
Today at 5:30 pm it was down to 3.5 Does that sound reasonable due to sun alone? Should I be doing an overnight FC loss test even if I don't have an issue with CC?