Chemistry out of whack after party

[sunkissed]

Hi -I'm new and posted in the wrong area, apologize, We got our chemistry numbers in line for our small community pool - chlorine level held overnight, ammonia - 0 , phos- 0 and opened it for the season. We had a memorial day party with a heavy bather load, many childern, adults staying late into the night. Althought alcohol is not allowed at the pool, an empty case of beer was found... i feel contributing to bather load... uhm... Our pool was build in 1972, fiberglass interior in 1992.

I had the Chlorine @ >8 prior to the party. The off-line chlorineator ran on high 24/7. The morning after the party the chlorine was 0 and the water was cloudy. I added 20 gal of 12.5 liq chlorine. The following day I had the water tested at our local pool store. fc -.5
pH - 7.8
Alk 165
hardness 275
cya -0
phos - 2500
ammonia -0
any idea what happened??? Do you feel I'm being too hard on the bathers?

I test FC, CC, pH 2x daily (required by State) using Taylor kit. I usually let the pool store run Alk, hardness, cya. I do not have the ability to check ammonia. We have an off line chlorineator, use 3" tablets, shock with liquid chlorine which was first recommended by our pool store and better understood through this forum.