I know combined chlorine is a culprit, but what are some other reasons?

PH at what levels?
Alk?
High CYA?

My PH was 8 a few days ago, and since lowering it to 7.6 I've noticed some eye stinging. I'm not sure if this is the cause, or since I only have an OTO kit for chlorine perhaps I'm starting to get a bit of CC. One day I'll have Ben's kit and won't have to worry about this any longer.

Thank you