Customer's bather load crashed her FC faster than I've seen in years

Tampa, that bump-the-target-up approach is exactly right and matches what I've seen with my own grandkids using the pool for a weekend. The one thing I'd add is it's not just bather load eating chlorine directly, it's what they bring in with them. Sunscreen, lotion, sweat, whatever's on their skin, all of that is organic material that chlorine has to oxidize same as it would algae. So a graduation party isn't just raising demand through numbers in the water, it's dumping in a load of contaminants that burn through FC fast and then you get combined chlorine climbing too, which is part of why the water can smell off the next day even though your FC reads low rather than zero. I've found bumping FC to around 8 or 9 ppm the morning before a known heavy-use day, assuming CYA is in the 30 to 40 range so you're not wasting it, holds up a lot better than trying to chase it down after the fact like you said. CYA conversation still matters, it just has to be paired with knowing a party weekend is coming.

Alan's right about the organic load but nobody ever checks their return jets and skimmer flow during a party like that, with that many bodies displacing water and kids hanging on the returns you're not circulating near what you think you are, so that fresh FC dose isn't even making it around the pool evenly before it gets eaten up.

Dave, I don't know about the circulation thing being the real culprit there, every party we've had here it's still a screened cage and a pump running the same cycle it always does, and I've never once noticed FC sitting unevenly around the pool after a big swim day. Bodies in the water slow things down a little sure, but chlorine demand from all that organic load Alan's talking about, that's happening everywhere in the pool at once, not just in some dead zone by the return. I'd put my money on the sunscreen and sweat load before I'd blame flow.

What gets me every time is how fast a pool can go from boring to busy. We don't get six grandkids over here but even four or five friends my wife has over for a swim morning, by the next day FC's noticeably lower than a normal week where it's just me doing my laps at sunrise. Bumping the target up before a known heavy day like Alan said is the right move, chasing it the next morning is just always going to leave you a step behind. Good luck with her, sounds like you've got her pointed the right way already.

Chuck, before you write off Dave's circulation point, what size pump and how many hours a day is she running it. That's the piece nobody mentioned yet. A single speed on an eight hour cycle built for a quiet pool with two adults is a different animal once you've got a dozen people in there for six hours straight, you need more turnover that day not the same schedule, and a lot of these residential setups are already running the bare minimum to keep the water legal on a slow week.

Dave's not wrong that flow matters, I just don't think it's dead zones by the returns so much as total turnover not keeping pace with that much demand hitting the water all at once. If she's on a single speed and running normal hours, bumping run time during party weekends is probably doing more for her than bumping the FC target alone.