Hi guys, So I've got a few Bonsai which include a Chinese Holly, A Drawf Rhododendron which I potted myself and then a couple of weeks ago i went into a local garden centre, smelt this azalea bonsai as I exited picked it up and brought it. When in the car it had a few yellow leaves, when home I cut off the yellow leaves and had a look around the tree and was quite happy about my purchase. Presuming the yellow leaves was from it being kept inside and maybe under watered ?

So forward maybe a week and a couple of days and i have started noticing all these red tips appearing on the edges of the azalea's leaves. initially i thought that it might be some sort of pest like lace bug or aphid or something but I have searched under the leaves and i found one black looking insect didn't move when touched it, that was enough or me to quickly make some soap spray and give it a good going over, all over the leaves including underside then rinsing off with normal water after.
Now its been two weeks more leaves are getting these red tips and seems to be spreading around the edges, Not to sure whats going on as the rhododendron isn't doing this and it close to the azalea. In england where i live its just finished a heatwave where it reached 30 for a couple of days and has been quite humid, not to sure if that is a factor. Tree is kept in shade for most parts of day with a morning misting. and watering only when top soil is looking dryish and little dry to the touch.

Any help is greatly appreciated if you have any idea's on what it is and if its normal for late july.