FC …should I be concerned

[Laziebun]

So I took a water sample last night at 9:26pm and had
FC 12.5
CC .5
CYA 80

Took a sample this morning at 5:38am
FC 8.5
CC 0
CYA 70

I do have this logged if anyone wanted to take a peek. We did take a dip in the pool from 4-6pm

Wondering why my FC dropped so much..?

 

[Newdude]

Was this mornings sample well mixed first ? Was last night's sample well mixed?

If so it may be a fluke occurrence after a long swim. (1-2 would be more 'normal'). Keep the FC clear of minimum and do another Overnight Chlorine Loss Test tonight. If it repeats you likely have the onset of an algae bloom and need to SLAM Process

*edit. It's likely leftover algae that either was not fully killed last time, or reintroduced from a hiding spot afterwards. (Ladder rails, light niche, etc)