Pop up cpm dropped 45%

Yesterday my cpm on popups with clicksor was $2.07 on 2,931 traffic,and today on 919 popups my cpm has dropped to $1.14. I have them set to display every 6 hours per visitor,and so far its only 6:34central time USA.

Is it dropping because of the lower quality traffic I have gotten so far today, or is it because I have the popups set to display to often?

My CPM pop earning in August is stable. I can earn around $10 for average 5,000 impression.