Time to SLAM! I've consistently maintained FC of 7-8 for my CYA of 40 using pucks. I had a leak that I fixed and tested CYA again to learn it was 25 last weekend. So I added 1.5 quart by volume to raise CYA to 50 which my pool seems to like given all day sun. Last night I measured FC at 5 and for the first time in a long time measured CC less than .5. I never have any CC, sample never turns pink.
This evenings results, and this is to illustrate how fast it can happen?!
CYA 55, maybe 60. I measured indoors with a flashlight
So what happened? I let FC get close and possibly below minimum and more sun/heat. I got complacent. The first indication should have been the presence of CC which I never have in my pool.
This is the first time I have had to SLAM outside of opening/closing so I blame myself. But hopefully others can learn to test frequently and if something changes in results, act quick. Thankfully I can act on this fast and should be OK. Nip it in the bud.