Definitely my takeaway as well. I was a little surprised someone didn’t chime in on this thread recommending drain/refill though.4”? Gross. Do you have a picture?
6 people is a lot in our 450 gallon hot tub, and nobody is wearing sunscreen. 18 people in a 2200 gallon pool all wearing sunscreen to the point you had a massive ball of it in your skimmer? I suspect this was just a massive load on the chlorine, and oils don’t break down nearly as easily as typical bodily wastes (sweat/etc).
The guide for temporary pools (~3000 gallons or less) does indeed say this. I’ve recommended it as an option to people with Intex style pools even bigger if water is cheap. One time I let my 450 gallon spa get out of wack because I forgot to add chlorine after a night of partying, then forgot the next morning and the next two mornings. Water became cloudy. I tried slamming and after a week or more I still had some nasty CC’s and ended up draining and refilling anyway with the usual Ahh-Some purge. So I will never try to SLAM a hot tub if I let the water get that far out of wack again (which hopefully I will not do!).