We recently opened our pool and are having a problem with combined chlorine and ammonia. I have a 33,000 gal vinyl in ground pool (fc 0.5, cc 5, pH 7.2, TA 140, CH 160, CYA 0). I can't get the FC level to budge above 0.5-1.0 and the combined chlorine is reading 5+. Based on discussions on this site I decided to check the ammonia level which reads about 6.0-8.0 (I admit to letting the pool go over the winter and opening it late). To get rid of ammonia it has been suggested to shock to 10x the ammonia reading, so in my case 60-80 ppm. In a 33,000 gal that's a lot of chlorine!
A coworker told me that non-chlorine shock (specifically potassium peroxymonosulfate) can be used to destroy ammonia. Is this true? If so, are there any drawbacks? It might be preferable because my understanding is that it will start destroying some ammonia without having to shock to the 60-80 ppm breakpoint and it would be safe to swim shortly after application (which is important since company is coming for the holiday weekend.
I apologize if this doesn't make any sense as I'm still trying to get my head around the chemistry. Any help and input is appreciated.