I've dropped from an average of 1.8% to 1.2%. That's down by a third!
Is this a bad thing?
If CTR was what i was most interested in then I'd be concerned.
Many people would be very worried about this change.
However, here's the important thing.
Over the time period I spent the same budget every day and the clicks did this:
For the same budget, the number of clicks went from an average of 184 to 290. That's an increase of 57%. This is a very good thing.
On its own, CTR is a potentially misleading statistic as it doesn't show the whole picture. Without knowledge of the number of impressions CTR is meaningless. A high CTR from a low number of impressions could be a lot less than a low CTR from a very high number of impressions.
My ultimate aim from buying the advertising is to increase the number of downloads I get. Clicks are a proxy for this figure as the store won't yet tell me where referrals come from. Without the store listing changing over this entire period I can assume that the conversion of people clicking on the ad to eventually installing the app has remained constant.